Get a good strap, get a decent amount of storage (make sure it's the appropriate read/write speed), spare batteries, a flash (or flashes if you want to get fancy), filters, lenses for whatever you're intending to shoot (primes can be fairly cheap while still producing great images if you're just starting out), maybe a tripod and remote trigger (especially if you're doing long exposures or something).
Also, carry a trash bag or three to function as a cover in the rain, gear protector, poncho, or other duties as needed.
