http://www.thesaurus.com/browse/tomboy
I don't really think there is a good synonym for "tomboy." I do think it would be fun to have two coordinating kits called "Something Other than Pink" and "Something Other than Blue" with a tomboy theme and a girly-boy (if that doesn't tell you something -- we have a nice word for girls who like "boy" things but no nice word for boys who like "girl" things) theme.
--says the mom who has a daughter who loves to camp & play video games and a son who loves My Little Pony & helping cook