Hi,
Looking trough the pkgsrc tree I see some changes in gnome packages since I've last instaled it, but for the base installation should work
gnome-session.
Probably you will also make use of
gnome-menus and (don't know for sure it's necessary)
py-gnome-menus.
Of course You need also all dependencies
.
Meta-package Gnome includes not only base packages but also lot of applications like web-browser etc. It's good while You are using gnome-like application, if not I would go only with bases.
Tom