You probably already have 50 ways to remember the difference between complementary and supplementary. Here's one more that I made up and I think it's pretty cool. I recognize that it's very possible (although unlikely) that someone else also make up this trick somewhere in the universe. Let's just hope that I came up with it first.
I always tell my students to take the co in complementary, and simply draw a line on the c so that it becomes 90. Therefore, complementary angles add up to 90 degrees. Supplementary doesn't work as well, but I like it anyway. Take the su, draw a 1 next to the s, put a slash through the s to make it look like an 8, and top off the u to make it look like a zero. Voila! 180