Am I right thinking you are both women?
Not to everyone's taste but a beauty type evening, do each other's nails, hair, sip champagne.
Both buy an outfit for the other to wear. You have to wear it no matter what. You don't tell each other, you just get given a bag / box and go get changed in separate rooms - it could be something nice that you wouldn't normally see the other in, it could be fancy dress, it could be anything.
Obviously this can be extended when you have children to include them.
Start something that can last 30+ years, maybe a new decoration or something for the tree that you can add to each year.
Are you a soppy couple? Write a not to each other saying one thing you have enjoyed about / with the other this year - after reading put in a jar and add to it each year.
Have fireworks?and/or a barbeque.
Go to the cinema and for pizza after - this can be adapted when you have kids so when little it might be a film at home and frozen pizza.
Order from a take away you have never used before, preferably a type of food that is new.
Buy and play a board game.
Pretend you have kids, each buys a toy that needs to be assembled and removes a piece, the other has to try to assemble it, without instructions. Add wine and trying to keep quiet.