I was a homesick child. Send a lovie, have them pick it. Something small. I would sleep with it inside my shirt to comfort me. I had so much fun during the day, but evenings/night was always really hard. Thankfully I was also pretty tired so I'd fall asleep quickly and in the morning I was fine.
My mom would mail me letters before I even left for camp (it was only a week) so that I would get a letter on Monday (camp started Saturday). I didn't realize until I was older she did that, but I always LOVED getting mail and it helped a ton. I'd write her too, which is funny, because it was only a week.