Crafts - Oriental Trading has lots of crafts that will work for your son's class.
Games - Our first graders have enjoyed bean bag tosses, hot potato, ring tosses, pin the tail on the donkey. Most of these games can be customized to fit the holiday. Use heart shaped bean bags, heart shaped "rings", pin the arrow on the heart (using sticky tac or tape), etc.
Recipes - Wilton has a heart shaped cupcake pan if you really want to get ambitious. There's also lots of heart shaped cookie cutters. Kids don't really care - just use plenty of sprinkles!!!
We also have gone to juice boxes or koolaid bursts in the classrooms. Our PTO purchased new carpeting last year for all the classrooms. The juice boxes are less likely to spill than an open cup.