A good way to remember flat keys, especially to those playing a 5 string bass, is by remembering the notes at the first fret of each string. So they only need look quickly at their bass to see what the key would be, e.g the first fret on the B string is a C, E string F, A string Bb, D string Eb etc, and remembering that it starts with none, then one flat, then 2 etc.
Sharp keys are the cycle of 5ths, so start on the same C, move up in intervals of a 5th, so up a string along 2 frets is 1 sharp and G, up a string and along 2 frets is 2 sharps and D, etc.