It's a pretty depressing question, but the answers people have come up with seem to be good. Maybe with enough invisibility rings in the world, "monsters" will at least be able to move from one Avalon to another with the right helpful moving company. 

She's in the mood for a snack; she'll check out that frozen yogurt place.

It has a lot of flavors! French vanilla, Belgian chocolate, triple berry, passionfruit mango, taro, sweet cream, mint chip, raspberry stracciatella, coconut, almond praline, bananas & cream, cake batter, Oreo, cookie brownie cone blast, oatmeal raisin, cherry ripple, honey lemon, strawberry kiwi, and mudslide. They also have sorbet in pineapple, raspberry, pina colada, orange, peach, lemon, strawberry basil, and papaya lime.

Excellent! She'll get half Belgian chocolate, half raspberry stracciatella. Then she'll eat it on a bench outside, in the crummy excuse for sunlight that won't melt it as fast as the real thing would.

This Avalon is a little more crowded than the Boston one; it does serve a wider area, and Seattle's a bigger city, and it might be a bit physically smaller too. There go some kind of lion that way and some kind of equine that way! Here come wings and there go tails!

People-watching is super fun! She should look for a new gaming group or a book club or something, get some critter friends in the new town and start in on having a social life before school starts. When she's done with her ice cream she'll wander around some more, keeping an eye out for interesting flyers and/or jewelry shops but mostly just exploring.

There's a bulletin board, near the entrance. It advertises:

- GURPS superhero campaign needs one more player
- auditions for a bassist for a band ("monsters OK if you can hide with a wheelchair or something for outside gigs")
- delivery driver and loading/unloading jobs; price of driving lessons included if necesary
- coffee tasting event
- a faun author will swing by the Avalon bookstore to sign things and read a chapter aloud
- Critter Babies Playtime Meet
- Thai cooking class
- knitting circle ("NO CROCHET PLEASE")
- ships in bottles / model trains / miniature painting / dollhouses / kitbashing / etc. meetup calling itself "Small World"
- Seattle Avalon Film Festival deadline upcoming!
- Cardboard box maze construction in the park ($2 or help with breakdown afterwards)
- High tea
- Community choir ("ESPECIALLY TENORS!! but all voice parts are welcome")

There's also a shop with accessories - not just jewelry but also phone charms, cute socks, hats, watches, water bottle holders, fanny packs and more dignified belt pouches, tiny backpacks, clutch purses, fans, umbrellas, novelty glasses, sunglasses, scarves, fake flowers, and belts. The little shop is very densely packed, but some of the displays are on wheels and larger customers are pushing them aside to get by one way and then pushing them back to go down the next aisle. The store is called "Hornaments" and is operated by a glaistig.

GURPS, huh? Well, she shouldn't knock it until she's tried it. She notes down the time and location for that, plus contact information unless it's drop-in. After some thought she also writes down the info for the cooking class and the cardboard box maze.

She wanders through Hornaments for a bit, not really looking for anything in particular--say, are any of those belt pouches made of stiff enough leather to be basically rigid on the outside?

Yes, this one is! It appears to be present in Hornaments on consignment.

She checks the price and asks the glaistig if she knows where to get more of these.

"I think someone got it at a renfaire and then decided to minimalist her closet, but I couldn't tell you which faire or what leatherworker, sorry," says the proprietor.

"That's alright, it's nice even if it isn't part of a set." She'll buy it unless the price is ridiculous.

It's $55.

More than she'd spend on it for herself, but she expects to be able to sell it for a hefty profit, and if she somehow can't it's still a nice pouch. She buys it and wears it out rather than bother with a bag.

"Come again!" calls the glaistig cheerily.

"I might well! Have a nice day!"

Now that she has something to do at home other than be frustrated at that jewelry bag some more, she wants to get on with doing it more than she wants to wander the Avalon. She steers for the exit.

It lets out into a warehouse section of Seattle, with a critter-operated private athletic club nearby to explain all the traffic and provide parking (also treadmills).

That's pretty clever! Margaret heads home and examines the leather belt pouch more closely. It has a flap with a clasp instead of a drawstring, of course, and it's made of stiff leather instead of flexible fabric. There aren't any gaps in the stitching large enough to be likely to count as extra openings.

Yes, this should do nicely.  "Replace the space inside this bag with a cubical space six inches on a side, without affecting the outside of the bag or the part that opens and closes except that it will open onto the new space." Last time she used this variant it made the outside of the bag rigid but the inside did what she wanted.

Indeed, the pouch is now rigid - it already was, but moreso - but the inside does what she wants.

Excellent. How's the shape of the interior? If she turns the pouch over, does the space on the inside rotate with it?

It is a six inch cube, and does rotate with it.

Excellent! She puts a few pieces of paper in it, closes it up, and sets it aside, then turns to the variously-sized cardboard boxes conveniently scattered throughout her room. She already has a pretty decent spell text for expanding boxes, but she doesn't actually know if she can sell them to Avalon residents yet. She grabs two boxes that already easily fit one inside the other and expands the space inside both of them by a factor of two. Then, again standing well back, she tosses the smaller box into the larger. At this point she's pretty sure she isn't going to create a black hole in her bedroom, but it's the principle of the thing.

She does not create a black hole. It appears to work just fine, though her aim is such that the little box clonks the edge of the big box on its way in.

She walks over to the pair of boxes. Are they both still bigger on the inside?

They are!

Yesss she can make bags of holding critters will be able to use! Assuming they interact with Avalons like they do with each other, and that that happens every time and not just when a dragon is doing it. Verifying either of those assumptions is going to be a pain in the neck; for the moment she amuses herself turning the small box right side up in the bigger box and sticking her arm way below the level of the floor.

The next thing she can definitely make progress on is figuring out how much space she can fit in a given space. She disenchants the big box and enchants the small one to have an interior four feet on a side.