We use plastic tubs with homemade cardboard dividers. As long as the pieces don't clink together when you move the tub you're good. The tubs have other virtues as well: they're waterproof, they both fit under the tables and stack well, when full they make ok seating, you can pack like things together, so its easy to see what you still have or what you need more of. One bin gets the cash drawer, bags, wrapping paper, table banner and so on.
You can pretty much assume that a shop will double their cost (at least). So if you want your stuff to move you have find the point where you are getting a reasonable amount for it, but the shop can still sell it. If the cost to the shop gets too high the pieces won't sell,mor they will stop buying. If that price is too low, you don't make any money. Figure out what you can afford to sell your work for-there are several good blog posts about that linked somewhere on these boards-before you go to the shop. Discuss this in detail and get a schedule of prices set in writing before you leave any product in any shop. If you visit later and find they have increased the selling price, your commission wil have gone up, so that's ok. If you are wholesaling, you can then discuss changing the price you get.
I got my start by helping friends who needed another warm body at events. Some events are so big that having two people to make sales, wrap, chat up passersby, etc. is a necessity.
Having someone you trust to watch the cash box while you go pee is very nice. And if it happens to be slow you have someone to chat with.
We sell mugs in sizes ranging from 1 ounce to 188 ounces. The tiny ones get people to stop and look, and the giant one is used as the end of any request for a bigger mug. First we go through the smaller ones, then we unveil the big one, and they laugh and buy something.
If you enjoy the company and interaction with other artists you might enjoy being a partner. The community aspects of a co-op are as important as the cost/benefit ratio. There could be ways to maximize the usefulness of being at the store-advertise the the artist on duty and have some work in progress that folks can ask about . Pump up your sales by show adding your work on those days.
And if you get your buy-in payment back, you could try it for six months and see how it works for you.