It's better to see what your cousin likes. If you send regular gifts, you can send some festive gifts, such as black tea sets, auspicious ornaments, personalized couple dolls and so on. I think anything that can mainly express a hundred years of harmony and grow old together should be ok.

For another example, you can also send some commemorative gifts, such as personalized gifts (it seems that anyone who has their name or wishes them can at least show that you are aiming at them and are especially careful! )

I hope it helps you.