I usually give a baggie with the quilt that has one or two extra blocks and some extra bits of fabric, with the instruction to hang onto these in case of damage. So that there is fabric to complete repairs.

I never make just the right number of blocks. I am always generous with the intention of using them as "seed" for another quilt.
The key word being: "intention" - - best laid plans of mice and men, don't you know <g>
ahhh, welll .... I have a lot of blocks for samplers if I ever get to them, eh? LOL <wave>
I totally buy my daddy's idea of having dinner guests: If you don't have leftovers, you have not made enough
I mean! I TOTALLY keep that in the back of my mind for whatever I am working on ;-)