For anyone in the US who is interested in those collection cases sensui posted about a few pages back, you can buy them online from the California Daiso here. They only sell stuff online in bulk, though, so you'll have to purchase them in multiples of ten. 0.o Also, they only ship UPS.
Alright, thanks. I should go check my campus post office and see if they provide the materials. What about shipping labels? Does the post office print out the First Class/priority mail shipping labels? I see options for paying online, but…ah. Maybe I should stick with stamps. loll
If you get in line, you're going to have to have the addresses already written out on your package. The post office usually provides free sticky labels for priority/express mail. With first class, you're on your own.
If you plan on shipping priority mail, I highly suggest using the small flat rate box (I'm assuming most things you're selling will be smallish, right?). The small flat rate cost about $5 to ship in the US (it's whatever the lowest cost of priority mail is) and is about the size of a medium-thick paperback book. You could fit several of those small keychain-type figures in there, it'd cost the same amount, and they'd be nice and snug for shipping. The same boxes can be used for international mail, and cost about $13.
If you need a bigger box, there are also two kind of medium (shirt box size and shoe box size) and a large flat rate box. Of course, assuming that the stuff you're selling is light, you're better off shipping by weight than using a flat rate box for that size. The post office also provides a priority mail non-flat rate box for free that is about the size of a shirt box. Just make sure it doesn't say flat rate!
If you buy postage online, you'll save a few bucks, plus you'll get free delivery confirmation for priority mail. If you're not spot on with the weight, it doesn't matter, but you can't try shipping a 5 pound box at a 1 pound price. You also can't buy first class online.
Some post offices have automated shipping kiosks, but even those don't print out the address–just the city, state, and zip code. You've got to fill out the rest on the sticky label that pops out. Also, you can't do international shipments on the kiosk.
If you ship international, be sure to talk to the recipient about the best way to ship. For example, I once mailed a plushie to Italy, and the girl who bought it asked me to ship it registered mail, or she'd never see it. You can only get registered mail on first class, and you can't have tape or anything on the edges of the package, because they have to print something around the edges. Found that out the hard way. >.<