THIS PAGE IS OUTDATED! Now, you can now break and place blocks with the proper tools, so tools are NOT useless.
This means that, you don't need to find an NPC village. I'm doing quite well with my "Generate Structures" turned off.
I've been making creepers blow up one or two trees to get enough wood for a crafting table and an axe (not so hard), and then using the axe to get enough wood for picks, swords, hoes, and shovels.
Note: Spend your first day getting food (you'll need it since creepers are going to be exploding on you). When you hit a mob while falling, in any game mode, it deals extra damage, so fighting mobs while jumping is a good idea to get you through your first, weaponless, night. During the later nights, if you don't have a sword for fighting mobs, your axe is just as good.
Use swords to get leaf drops.
Theoretically, you should be able to do as much in Adventure as in Survival! (Though, to get to the nether, you MIGHT need to explode TNT to light up the portal. Haven't tried yet.)
By the way, if you're on Peaceful, then... yeah, you gotta go to the nearest village. Sorry.
- EDIT: Fixed it.
- (By the way, I don't know why I said you have to explode the portal. Flint and steel works just as fine. Maybe I thought you needed your bare hands to get flint, but you don't.)