We know that Kreacher told Regulus Black what happened in the Horcrux Cave. It seems to me, then, that Regulus Black could have better prepared to go to the cave and not doomed himself to die a horrible death if he'd just done one or both of these things:
- Brought some water with him to counteract the horrible wasting thirst from the potion until he could get back out of the cave and get help, like Dumbledore.
- Side-along apparate away with Kreacher out of the cave, since elf magic is not limited by the cave, as proved by Kreacher's apparition when called.
It seems like such a simple solution to avoid death. Why didn't he do either of those things? Was he just not thinking clearly, or am I overlooking something here? Is there any canon explanation?