How do I assign individual keys/keystrokes?

I find I use 'and' a lot in my entries, and want to use the '&' but this means I have to invoke the 123 screen and then tap on '&' - its nearly as quick to tap 'and'. I thought maybe I could map the '&' onto a slide so that I can access it from the main screen but could not find the '&' in the Custom Slides dialogue. Any suggestions?