This is very warm-hearted of you!
Without knowing anything about his condition, it's hard to say what he could use right now. If he has burns to his face/mouth, I'd avoid chapstick since the hospital is probably using whatever's appropriate (we use bacitracin on my unit) while the skin heals; a lot of scents/flavors are irritating to fragile skin. We splint patients' hands after grafting (if they were burned on the hands) so they aren't able to use their hands for a while (usually several days) and then after that physical therapy/occupational therapy starts working with them...I'm trying to think of hand-operated toys that also encourage range-of-motion or strength? (I work on an adult unit & don't have any kids!)
Since I don't know (and you may not know either) how he's doing or when he'll be awake and interacting (if he's currently on a ventilator), I would avoid anything that spoils (food, flowers--which we won't allow on our unit anyway because of insects), money or gift cards
(too much time for stuff like that to be lost or "lost"; if the family has a website you might be able to donate directly that way), and giant stuffed animals that take up a lot of room and are impossible to keep clean.
Depending on what you know of the family & patient, maybe he'd like some comfy but cheap sweatpants or pajama pants (if no leg/groin burns) to wear and they can be tossed when dirty (burns drain...a lot). Or some books by a favorite author/on a favorite theme, to either read or be read to him. Or some non-perishable treats that aren't purely junk food. Or a card every day for a week? 2 weeks? that says "I don't know you personally but I care about you! I'm thinking of you as you heal!" and similar sentiments each day.