V3 itself, textures probably (there are some freebies, mostly fantasy-themed ones, and DAZ offer a file that, used with the free UVMapper Classic, lets you create a version that can use V1/2 textures), body morphs and head morphs (more-or-less essential). Most prop-type V1/2 hair (the stuff that goes in the Hair library) will work with V3, though the ears are in a different place which can require some tweaking, and there are a couple of free poses that will make some conforming hair for V1/2 work too. Clothing is trickier: if you have the Tailor (Windows only) there is a method for converting V1/2/Stephanie clothes, and there are some freebies.