During my first Mun landing after I bought the game, I realized I may not have enough fuel to get my precious Kerbals safely back to Kerbin. For some reason, I stored 8 Oscar B's and Toroidal tanks onto the side of the lander. Once I landed on the ground, I had quite a bit less then half fuel left in my main tanks and I kind of panicked. I turned off some backup mini radial engines because they used too much fuel (I also hate their sound) and lifted off, transferring fuel to the main tanks on the way. Miraculously, I had enough fuel to not only get into orbit, but also do the transfer. By the end of the whole ordeal I had little more than 1 unit of fuel and I was safely on Kerbin.