I'm a teacher-- I teach K this year but have taught up to 5th other years.
In my K class about half of the kids bring in something from home, either homemade cards or cards/candy or pencils or something of the sort. So that no one feels left out, we let each kid make a mailbox and then we pin them to the walls all around the room. All week, we work on making handmade cards for every kid. So every student gets a list of every kids name and they check them off as they make them-- the kids names are Word Wall Words in our classroom so they love writing out and recognizing their friends names. Also, this week we add "to" and "from" to the word wall so they can write that on the cards. On V-day (or this year, Friday) they get all the cards they made plus anything they brought from home and they deliver them to everyone's mailbox around the room-- fun because they love finding the boxes and recognizing names. Kids don't feel left out who didn't bring in anything else.
When I taught upper grades, my favorite thing to do was print out valentines for every kid from every kid, then on the valentine they were required to say one nice thing to every person on the card. If they weren't friends with that person, could be as simple as "you are good in math." I stressed how everyone in our room is good at different things and has different talents and personality traits-- and that if you were stuck trying to think of something for someone, watch them for a few days to see something that makes them stand out. Then after we deliver the cards we glue down all the things people said about us into handmade notebooks. The kids absolutely TREASURED these, and it opened up so many great lines of communication, esp for kids who feel as though no one notices them. Weeks later I'd still see them pulling out the books and smiling re-reading them.