If you can't have more than a ten gallon tank at school, I would suggest looking at getting a bigger tank for Odie soon as you might have to leave him at home once he outgrows the 10g. That could happen much quicker than you expect.
I hate to be a bearer of bad news, but goldfish really make pretty poor beginner fish. People assume that they can be kept in small tanks (or even unfiltered bowls) and do just fine, but really these fish need pretty big tanks (30 or more gallons per fish for adults) and tons of filtration along with big weekly water changes.
I think you should do some research into smaller fish that would be more appropriate for a ten gallon tank. For most tropical fish, all you'd have to add to the setup you've got is a heater and you'd be all set. Sure, there are the standard assortment of small schooling fish like tetras, danios, barbs and rasboras, but there are plenty of other interesting fish you could easily keep in a 10g that you wouldn't ever need to upgrade tanks in order to keep. Dwarf puffers, bettas, various kinds of killifish, gudgeons, dwarf cichlids...you have tons of options.
In terms of tankmates though, goldfish are somewhat difficult to find appropriate tankmates for, considering that they're coldwater fish. Like was said before, shrimp and snails might get eaten. If you had a bigger tank, you might be able to house some white cloud minnows with your goldfish, but those could get eaten as the fish grows.