21st Birthday Gifts For Boyfriend

Which of these 21st birthday gifts is best for a boy??
I want to get my boyfriend an engraved 21st birthday gift, which item would be best?
a) A hip flask
b) a pen
c) cuff links
d) Your suggestion
(He already has a nice watch, so I can’t get him that!) Thank you so much for your help!!
e) Engraved shot glass
NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO sweeti dont get him no pen or cuff links he’ll act like he likes it but in his mind he’ll think what the hell is this. look trust me i know what you need to get him. u need to get him 2 things
1) get him a silver or white gold bracelet with his name or both of your names engraved or something romantic like “TODAY, TOMOROW, and FOREVER”
2) get URSELF one of those costamized thongs that has a writing on the front have it say something like “(ur bf’s name) enters here” or “(ur bf’s name) only” trust me hell love it… good luck