The gas will pretty much evaporate on its own, leaving behind the oil and other deposits. Just about any powder substance can be used to soak up the oil. Plain old dirt would work but I would recommend something like baby powder, something that is going to feel better next to your skin.
I bet your boots will be okay once you get the oil out. Your feet are pretty tough and as long as you wear thick socks they probably won't react badly to any residual petroleum products.
Your head is a different story. The padding on the helmet is much more of a sponge than you boots so it will be very difficult to get all the petroleum stuff out. You may get it dry, but any moisture will dissolve more and could create a problem. So, as long as your head didn't sweat you might be OK. But if you are like the rest of us your head will sweat like crazy in the helmet. At best your hair will smell like gas for a while. At worst you could end up with a major skin rash and irritation. Not fun.
If it was me I would try washing the helmet with a lot of dish soap and water. Like soak it in bucket over night. Agitate the bucket frequently. If that didn't work, I would get a new helmet
Rod