The most useful spare part is unimpressive until the ordinary one fails.

Spares earn nothing on the day you buy them. A fuse, a spare key, a length of cable: their value sits entirely in a future you hope not to reach, which is why they feel like clutter and rarely feel like an achievement. Most preparedness looks like waste right up until the moment it looks like foresight. That mismatch is why so little of it gets done.

Pick one small failure that would genuinely disrupt your week and see whether the spare for it exists. If it does not, the fix is usually cheap and takes an afternoon at most.