I flew for 1500+ blocks in every direction and didn't spot any chalk or limestone sticking out anywhere, just peridotite, sandstone, and granite as far as I could see.
I did spot some borax when I went in a random cave, but it's very far away, and I can't mine it with my copper pick, so it'll have to wait for tin.
I guess leather is supposed to be a bit of a struggle since the backpack is made with it, and there'd be no point in having the hunter's pack or sack if it was too easy to get leather, but still, it's very frustrating that such a basic material as leather can be so difficult to acquire.
Panning for shellfish would be a great backup solution for this exact scenario. Do I love panning, no. But I would prefer it to restarting in hopes of a better seed.