Your first resources will come from sifting, so after you have the cobblegen setup, you will want to get the sifter from Ex Nihilo.
If you are new to Ex Nihilo read on, if you know what you are doing then you can skip this part.
To get the sifter you will need to gather string. In order to gather string you will need to obtain a silk worm to convert leaves into infested leaves. To get the worm you need to make a crook
Use the crook on the leaves to get a silk worm, then "plant" them in some leaves to have the leaves change.
Then use the crook on the leaves to get string.
Once you have enough string you can then craft a sieve.
By sieving or sifting different items (gravel, sand, etc) you will obtain different resources. The broken varieties can be combined and then cooked to get resources.
NEI will show all the possible outcomes when sieving so if you cannot find a particular item, try searching NEI to see what you need to sift to get that item.
For more information on Ex Nihilo and the machanics of the mod, check out their wiki
SKCraft