In lieu of favors, place a card at every table explaining that you chose to donate money to a charity that has a lot of significance for the both of you. This is such a heartwarming and thoughtful gift, but be really careful when selecting the nonprofit lest you offend someone. You can get these on Etsy for $1 each.
When you're trying to decide what kind of wedding favors you should give to your guests, one thing you should consider is if they'll keep them. After all, it's such a waste of money if your guests are trashing the favors as soon as they get home. Here are some wedding favor suggestions that will make your guests think twice about throwing them away.
50 Wedding Favor Donation Cards / In lieu of favors / Wedding favor cards / Donation cards / Reception cards - the "Charlotte" by NostalgicImprints on Etsy https://www.etsy.com/listing/150283573/50-wedding-favor-donation-cards-in-lieu