@mametsuko
many gave advice regarding the amount. I'll say something on how one may give:

put it in an envelope and add a card. do not buy a voucher or something, just add a crisp bank note. the card should have a short wish/blessings for the couple, your name readable and identifiable and ideally have your address, since some couples will answer with thank you gifts or notes.

there might be a place to deposit the gift, a table or a basket where you can place it if you don't want to hand it personally. check how the other guests are doing it!

many people like giving something big and bulky or handmade. those gifts are all weird and most will be thrown out.