In my traveling life which has primarily been indoors, i have used reef knot (tie two ends together) and clove hitch (tie to a solid object). They're both easy to tie and untie. I also learned bowline (create a loop) and figure 8 (create a bump) a long time ago, but i haven't found much use for them and probably couldn't tie them without looking it up. Depending on what you're doing, it might be more useful to have a couple of carabiners and some bungees or straps, since those can be used to secure things much faster if it's raining or you are tired/hungover/whatever.