Well, I didn't have in mind replacing the Buick's water pump after a thankfully minor coolant leak/overheating event, so that's already blown some of the budget. But what I'd like to do:
Detail interior; vinyl, leather, fake wood, clean and shine it up; Febreze the carpet, clean the rubber floor mats. Despite the heat, I've started on this myself.
June: have the cabin filters replaced and the fan cage cleaned out. Last year my A/C seemed poor, and it wasn't the refrigerant; it was leaves and debris that had collected in the fan cage over 9 years. A/C here is too important.
July: 5500 mile/6 month oil change, to Quaker State Defy 10w30, to see if it will lessen my fairly minor oil consumption. Not sure what filter I'll use. Since the overheating event, I might move this up to early June.
Have some of the little running lights inside replaced: the lock switches on the front doors, the buttons for the Driver's Information Center, etc. Ideally, have the stereo taken out and sent off to replace the lights in it. (I know the lights don't affect the car's driving, and all of those switches/buttons work. But burned-out lights look and feel shabby, and it's something I have to look at every day.)
ETA: I anticipate that the clock on the Buick will roll over to 100,000 miles by Christmas; so that'll be an excuse for a celebration. (I can see me now at the restaurant: "It's a birthday party." "Oh? Yours?" "No, my car's. Can you get 100,000 candles on the cake?")