If you go online there are plenty of ways that are suggested for randomizing decisions during live poker where you don't have access to an RGN. You can look at your watch, you can pick suits etc. But I was searching for a method that was more concrete. I finally came up with that method but it's a little crazy.
I have memorized 86 digits of a random string that I generated. You can do this by taking any random number generator and having it produce a series of random numbers across a range that you like. For me it's 1-10 as that allows for a level of precision that is not too detailed that I would have trouble memorizing 86 digits. It took me two days to memorize all 86 digits.
When I'm playing, I mentally keep track of my place on this bit-string and then simply use the next number. When I arrive at the end of the string I simply start over. This isn't anywhere near perfectly random but it should be on par with any of the other suggested methods.