I have my list of LSAT vocabulary, but if I post it here, everyone would be like, "omg....you should go back to high school....you shouldn't be taking the LSAT...."
Whenever I encounter a double negative that gives me trouble, I rephrase it in my own words. PT46.S2.Q10 is a good example of this. You can rephrase "X is not indispensable" to "X is not essential."