Voice of many experiences here. The gaskets do have a ring sealing them from the bolt. There is no seal on the bolt from the oil and coolant passages that they go into though. You most definately want to use a sealer. My preference and GM'* is a teflon sealant with PTFE so that it remains goopy and seals well to stop any oil or coolant from wicking up the bolts.
RTV ....I'd use it in a pinch.
On the coolant elbows and injector o-rings, lube them with oil or vasoline to help them slide into place.