Leaky Pannier Bag
Most of my various pannier bags, saddle bags, or other bicycle luggage have at least one patch on them somewhere. Just the nature of their job means that something always ends up rubbing a hole in them at some time - a stray bolt head that was well clear of the fabric before the bag was loaded; the rack that its bottom edge rests against, occasional contacts with abrasive walls or the road.
So the repairs range from the temporary (Duck tape), to permanent (puncture patches glued on to rubberised waterproof bags; patches sewn onto duck cotton), to the re-engineering (my Ortlieb office bag has been re-enforced with a PVC strip glued to the bottom edge; when that wears through, I’m replacing it with an aluminium one).
It’s really important that you take care of these little problems as soon as possible. If you don’t, your bag can spring a leak that could cause traffic chaos along your route. Just take a look at this woman, whose bag’s leaking double-yellow lines all over the place: