Here's the version of GUMPS I use, taken from my instructor and Bob's instructors, keep in mind this is for a C-150
G = Gas, yup, it's ON, (only two positions, on and off, if you're doing a normal landing it's obviously been on)
U = Undercarriage, OK, right main tire is still there, no branches or anything hanging off it, if I have a passenger I have them check the left side.
M = Mixture, full rich
P = Primer locked
S = Seat belts tight.
Another slightly humorous version I've heard for the 150.
G = Gas, still got some.
U = Undercarriage still there
M = Mixture rich
P = Prop, still turning.
S = Seat belts on.
This is actually more involved than the factory landing checklist. It just calls out speed and flap settings.
Phil