Once it has happened to me, a few years ago: just driven 200 km's for a day-paddle with Willem Molengraaff, when I discovered the sprayskirt was missing. As it was in the middle of the winter, paddling without it was no option. Drive back home is an option; although not a very pleasant one.
But first Willem and I tried to find a temporary solution.
As we were quite happy with the result, a "sprayskirt" which functioned the whole day just like a normal one, we are happy to share the idea with you.
Just in case you ever...........!
The base for the solution is the survival bag, you carry along with you for emergencies, together with a piece of bungee and/or rope.
The first step is to cut off the bottom from the bag, thus creating a plastic tube.
This tube is attached to the cockpit-rim by stretching one double folded end around the cockpit. In the fold you apply, with sufficient tension, a piece of bungee and/or rope.
In our case the bag fitted, after some stretching, almost perfect to the cockpitsize of my kayak. As there are also bigger cockpits you can make the bag fit by cutting the bottom out under an angle instead, thus making the perimeter,along the cuttingline of the bag, bigger and thus making it fit to a bigger cockpit.
Next, you double-fold the other end of the bag for easy entering the cockpit. You can also cut off any accessive length, but we suggest to have at least 60cm of bag left.
After stepping inside the cockpit you can stretch your kayakjacket over the bag while tensioning the underside of your jacket properly. Having a jacket with double underside for the sprayskirt, is even more ideal as the bag can be put in between this, creating a completely watertigth solution.
This is all: happy paddling!
O, and just one more thing: Once you have a wet exit, the bag is easily pulled out from underneath your jacket while exiting the cockpit.
Only in case the diameter of your stomach is almost tight fitting in the bag, I should warn you NOT to use this solution as it can be dangerous in a wet exit.
Probably this can be solved as well by adding a release rope to the frontside of your "sprayskirt's"-bungee; just as in a normal skirt.