Whatever their interests are, when one son was playing Ice hockey there would be new skates, pads...for archery new bows, golf would be new clubs...For tech kids, new mouse, keybords, controllers, games, steam GC from gamestop is always a hit with my 2DS.
New sneaks, crocs, pj's or loung pant, wallets, elec shavers...
new bluray player with fav movies-these can stream everything on them, ie hulu,
amazon prime,netflix...GC for these services, I tunes GC, google play GC, Movie/event tickets...
ear buds, phone chargers, usb drives, mouse pads...laptops, phones if looking for something bigger $
clothes-find fav brands and shop around or outlets for great deals-my boys have fave surf wear and RL and such but I can always find great deals if I look- we get T's, polos,hoodies,oxfords... also Jinx.com for gaming clothes or think geek for unique t's. I found an "I am the stig" on BBC website for DS who is a big topgear fan.
We've done things like food dehydrater, box of new bedding (pillows,comforteres,sheets), new desk chairs, framed prints, oneshare of stock framed, new bows, new guns, car mats
Also fav food items-beef jerky, pistachios, fav chocolates
I am sure I can up with plenty more, that is just off the top of my head.