I have a tendency to go a bit wild with my money when I get it, so I've started buying the stuff that I need first. There's no point buying a $200 bridle if your horse has a perfectly good one anyway.
Does your horse need a new halter?
Do you need new breeches or jods?
Hoof picks are something that I always lose, so there's no harm in buying another one of them.
Ooh, what about a slick 'n' easy grooming block? They work so much better than curry combs and really help get all of that winter coat out.