Hi I have used colored clothes pegs, sticky tac and curling ribbon .
I am always careful to not damage any surfaces.
I also use (dollar store) colored magnets for the inside main door.
I usually bring some peel and stick window clings. (They can also be used on the bathroom mirror to decorate). Many people use a wreath hanger on the main door to hang things or tie pretty decorations to door nobs.
Have fun planning.
Hugs Mel