I could use a nice new suit.
A $500 Amazon gift card, just to sneak around all your restrictions. 
New phone.
A tablet, because I don’t really want one. Anything I really want I can get.
Or some really good classy wooden jigsaw puzzles. They go about $100 each.
Would a really high end dinner, with expensive wine, count.
L. Ron Hubbard (yeah, him) had a similar story in Unknown in the early '40s, where a guy was cursed by having to spend $100 a night in Manhattan, and was not allowed to buy things with it.
Really nice, used vintage Mickey Mouse Watch.
Snowblower.
(And I promise to clear the sidewalks on my street and all my neighbours drives!)
Assuming it can be spent in sections:
MTB upgrades (roughly $100)
Used BMX bike ($200-ish)
Biking accessories - new gloves, etc. ($75ish)
Scotch (guilty pleasure #1) ($100)
Beef Jerky (guilty pleasure #2) ($25)
Mostly bike stuff, but two things just for kicks.
Brendon
A new Behmor 1600 coffee roaster. Mine’s busted and I can’t be arsed to fix it again.
Fly rod
Books
A bunch of new home brewing equipment. I’ve got a lot of stuff that needs replacing and/or upgrading, so I never want to use it…but since I never use it, it doesn’t seem worth the money to replace it…
This.
Or this.
Guess I’ll have to flip a coin.
Can you make it $500.25?
Haircut and color. That’d only be like $120 but I need it so bad and I haven’t been able to afford a cut all year. I am dying under my hair mop.
I’d also get this star projector from ThinkGeek. I guess I’ll spend the rest there, too.
A new bike. Or given what the damn things cost, maybe that’s half the bike.
I could get some stuff for the house, but that’d be for both of us, so per the OP it doesn’t really count.
Bookcases. 
I’d probably add navigation to the existing system in our car. Yeah, we’ve got a stand-alone GPS, and we’ve got our phones, but sometimes I’d like it to just be built-in to the damn car.
A bottle of Highland Park 25 year old Scotch.
As good a bottle of single malt scotch as $500 would get me.
High grade chocolate and a nice shopping spree at my favorite used book store.
Two really good netstreaming devices.