What can I send him?

I was talking to my boyfriend on the phone today and he wanted me to send him surprises in my letters. I had no idea what he was talking about and I kept asking if there was something specific he wanted. He kept saying no but I just really felt like he already had something in mind. I've been sending him pictures of us along with my letters but that's been it. I think I might buy some scratch offs and send them in a letter, he said that would be ok. I'd like to send him other things but it's not like they can do that much while they're in boot camp lol. Do you have any ideas of what I could send that would still fit in a letter envelope?