Self explanatory, how long did you live in Hardcore mode, and what made you live that long?
For me, I used the Gravity Gun, Portal Gun and Backpack mods in my game to make it slightly easier to bear. After punching the trees and making the tools, I would look for cows to get leather and make a backpack. Then, I would start searching immediately for a cave, and mine anything I find along the way. I tend to keep my eyes sharp for an Enderman in order to get a few Ender Pearls to craft a portal gun, and for fuel to make it work, in this case I'd already have some rails and a minecart to trap it. I search for at least 4 diamonds for the portal gun, 3 of which are for a pick. I'd then obtain more obsidian after that to make a portal to the Nether, then get some glowstone, some more Ender Pearls, and then craft a gravity gun. But I never made it past this point.
And it would be harder for you now. Newer versions of the portal/grav gun mods add nether stars to the crafting recipe. Anyway I'd basically just start a huge underground potato farm and live out my life in boredom and I'd never die.