We've had a number of guests celebrating birthdays and anniversaries during their visit, @Chris232 . Usually we try to go the extra mile with the following items:
1. Hang a banner (Happy Birthday, Happy Anniversary)
2. Leave a bottle a prosecco or wine (if they're of age) along with a mini-cake from a local shop (sometimes w/ice cream).
3. Purchase theme balloons and a card from the local dollar store.
Everything is visible upon entry, so it is a pleasant surprise.
These are inexpensive (and some are re-useable) items so it, doesn't add much cost, but guests are normally appreciative!
P.S. Some guests are non-drinkers, so we have a bottle of sparkling grape juice as an alternative.