Originally posted by FissionChips:

A portal, and that's it.

If I'm actually looking for somewhere else to set up shop of some kind I'll take the necessary non-teleportables, copper for forge, iron for blast furnace, whatever - but anything teleportable is a portal away.

Of course mixed biome islands give you everything you need anyway, you can port a smelter and work your way back up quickly.

This, basically. No need to make it very complicated: everything you need (or almost everything) is one short portal ride away.