I always did find it weird that the only time we see a giant use any type of weapon is during the battle at Castle Black, when one used a bow and arrow with such force it might have well been a ballista knocking crows from the top of the wall. Actually I think the first time we met one (when Jon Snow was captured and being taken to Mance) we saw the giant using a club for some labor.
After those events though, they just run in with fists. I know plot convenience, but seriously, Wun Wun could have taken out the entire Bolten army with a proper weapon. Hell give him that dead giants bow and watch him turn twenty men into a shish kabob before going in with a club and knocking dozens of men in a single swing.
But oh well, plot convenience.