You can borrow him summaries or notes for exams, or you can teach him a skill you have that he doesn't have (or something he struggles with).

You can listen to him
Really listen
Most people don't listen
They talk
You could spend half an hour having a conversation with him, about him
Don't talk about yourself
Get past the superficial (how are you, how was college etc)
Ask him about his dreams for the future or his happiest memory
Paying attention is expensive, that's why it's called paying
He'll be grateful for it
Just a thought

Damn that’s good

weed

I like both @catfluff and @cakelover's suggestions, like cake said you're time is valuable so maybe just spend more time with him or just tell him how grateful you are. Take him somewhere nice that doesn't cost anything like the beach or a park etc. Maybe make him lunch or make him something else, like a nice drawing. DIY things are always lovely to receive because it means the other person thought about you and made effort to make you happy.

So, I took it all in consideration and made a thank you card with some IOU’s inside for him. I wanna thank y’all for the inspiration