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.
Tented Wedding Favor / Donation Sign - 5.5 tall x 4.25" wide in Calligraphy
Charity Favor for Dog Lovers. This is for a wedding but wouldn't this be great for any event! These adorable sugar cookie and dog treat wedding favors to be accompanied by a donation to your local humane society. Link included for a free print-able and for the dog biscuit recipe (homemade Peanut Butter Bites dog treat recipe)