If you run out of lube for your fleshlight, you can try to substitute shampoo or soap; however, the gliding quality isn't as good and can lead to a minor irritation to the male external urethra opening caused by friction.
The best substitute (and I've been using it for years) is good old fashioned olive oil. No burn. It has a fresh, pleasant smell; and leaves the skin of your cock and scrotum nice and soft! In addition; olive oil also has a "warmth" component that pleasantly leaves a warming sensation to the genitalia region that helps with erection and keeps you hard!
Olive oil, my frenz!
Olive Oil!