The one gadget I would strongly recommend is a VOR plotter - one of these...
Or a close relative - simply because it's a nice compact ruler / protractor that's hard to break and lives easily on your kneeboard, whilst if you really have to, is useable one-handed.
The basic principle of nav, particularly on diversions, are not to try and do anything too fast or too clever. If you need to divert, carry on en-route to somewhere known a few minutes ahead, or fly to a visible town a similar distance, or follow a line feature in a safe and vaguely appropriate direction. And plan not from where you are now, but from where you will be in a few minutes.
That means you can take your time, get it right, and not get stressed or confused about the whole thing. There are absolutely no prizes in PPL flying for handling anything except circuits and emergencies quickly - the rest you can take your time, burn a little more fuel, and then get it right.
G