Once again, the inner tube of my back tire has ridden round and the valve isn't at a right angle to the rim. So I deflated the tube, and worked it back into place.
The other thing I did yesterday; I was finding my Tracpac shoulder caching bag (which is, IMHO, the ideal shoulder bag for caching because of all the compartments) to be rather heavy. But it's been a long time since I went caching on foot, so surely I should be getting the bike to carry more?
I looked in my caching bag, and sorted out the things I use several times per day (such as the pencil) from the things I use rarely, such as the multitool. I put all the stuff I don't use often into a front bike bag (a bit like this). I can also put my iphone and car keys in there while I'm out (in a zipped compartment, so they'll be safe), so my shoulder bag is a *lot* lighter now. I've also put a shoulder strap in the front bag, so that if I leave my bike for a while, I can easily carry it with me.
I'll see how it goes next time I'm out.