I find this is always the hardest group to buy gifts for. You have many good suggestions here; I'll try to give you a few more I don't think were mentioned, depending on his interests and what he may already have:
- new sneakers, work boots or hiking boots
- high quality headphones
- sports watch with stopwatch
- jersey from his favorite sports team
- electric shaver/beard trimmer
- mini printer to print photos from smartphone
- a good pair of sunglasses
- a carry-on size spinner suitcase or other nice piece of luggage
- a GPS for the car
- a comfy featherbed or memory foam mattress topper
- guitar/guitar lessons
- Leatherman tool or Swiss Army knife
- poker chip set
- a good telescope (not a toy)
- fishing rod
- tent or other camping equipment
- mountain bike
If he has his own place or will soon:
- a George Foreman grill, panini/sandwich maker, or waffle iron
- Keurig coffee maker
- tools- cordless drill, screwdriver, etc.