Can to a hand ?
 

how can i attach this coca-cola can to his arm to follow the arm animation ? it's really hard to animate the can manualy about 500 frames

i think you just need to parent it to the hand joint.. or you could try a point constraint, though i haven't used that much yet.

a parent constraint should work and you can have the character swap hands or place it somewhere and 'let go' of it by reducing the weight value.

If you don't intend for the character to let go of it then just use a standard parent to the joint as arran says which should be fine.

Gio

I make it parent .... render 360 frames .. on the 361 frame i get it out of the group and make a gravity field .. and it worked just find :)