Throwing a party is one of the most obvious gift ideas for an 80th birthday. Even if the guest of honor doesn't want a big fuss made, he or she will enjoy an afternoon spent with dear friends and family.
Invite people you know the guest of honor hasn't seen in a while.
Keep the party low-key by only serving desserts and coffee or punch. Guest will be able to mix and mingle without worrying about a sit-down meal.
Set up a table filled with old photographs to give everyone the chance to look back at the guest of honor's life.