In reply to Wildabeast:
A 10 year old Garmin Geko will do all of those things for 25 quid or so. Its more modern replacement is the Etrex10 for about 70 pounds. Both will run off two AA batteries for a long time.
Neither of those have any kind of useful built in map, (the Etrex 10 might have Geneva marked but that's it!) but if you already have the map and are just checking co-ordinates or following your snail trail back, they will work. It's easy to put in a list of point-to-point co-ordinates you work out in advance from a proper map.
The black and white screens of these things are readable outside.
The Etrex30 has maps but you'll need to buy local maps which may or may not exist for your area. They might not be very detailed, but you can load them in advance. There used to be a PC program for uploading & drawing routes onto the device called "Basecamp", I don't know what it's like now, when I last used it, it was a travesty of modern software design. Perhaps it's better now.
The built in map uses open street map which can be very detailed if people have drawn that area. The version in the GPS might be out of date but can easily be updated. This map is free and has world wide coverage. You can easily see what the coverage for the area you are interested in is like here:
https://www.openstreetmap.org
The detail on that map can be superb but it can also be inaccurate so watch out. The flip side of that is if you find a mistake, you can update it. You can select which type of layer you want (topographic, cycle tracks, ski runs etc.) I forget which the one used on the Etrex is.
You can get the same sort of functionality on a phone app these days, eg Viewranger, both with the free Openstreetmaps and paid national mapping agency maps. See the article in the latest Summit magazine. Of course, a phone might croak out in the cold or wet, doesn't work with gloves and might be hard to read in full sunlight.
For me, Etrex 10 is a perfect back up. I'm sure the staff in Cotswolds can show you other devices and you can get a feel for what works for you.
Post edited at 22:26