I ended up gettin past the Cave.. had to fight The Pain without getting hit, which surprisingly wasn't all that hard since you just Grenade him to death.
Later found some Serum along the cave walls, hah.
Grrr... well, I'm glad I found it after a while, but still... was quite an annoying situation.
I usually save multiple slots if I can detect something like that coming up, but I was in a pickle even w/ the Ocelot fight where I had saved with a lack of ammo/health - took me a little while to beat him (again, couldn't really get hit due to small life I had left). Once it was over.. I thought, "FINALLY.." but then I saw I was poisoned, haha.. so that had me fuming.. and when I came up to The Pain, I thought, "...you GOTTA BE KIDDING ME. When does it end?!"
Ah well. Thankfully I didn't have to restart
I hope the story in this one is as twisted as MGS2. It took me a while to get into MGS2, but when the story started going into the whole bit about The Patriots, that's when it started to shine.