Good lighting, small skimmer or hang-on filter with media, small powerhead(s), substrate (sand or other), live rock (10-15 lbs), heater, glass scraper, thermometer, hydrometer, test kits, syringe, turkey baster, nets, clear plastic containers, tongs, gloves, salt mix, RO water (if you're fussy), mixing bucket, extra powerhead for mixing, plastic tubing, and some old towels.
And maybe some duct tape.
Oh, and a 20 gallon would be better - easier to maintain stability in water quality. Plus there's some good 24" lighting fixtures.