Having just survived treatment for oral cancer I have used numerous dry mouth remedies over the past 21 months (and probably will for ever). Water is the cheapest of course, followed by "no sugar" chewing gum (keeps the saliva flowing which protects the teeth and gums).
Oralieve is very good BUT expensive (you might get your GP to prescribe it, otherwise buy online) and I didn't find the effects to be very long-lasting per use. I also found the taste to be too strong so I thinned it down with a bit of water. The taste might have been due to having a v sore mouth during/after treatment though. The soreness is much less now but I'm managing best with chewing gum and water - never go anywhere without the latter.
Avoid anything with sugar in it.
Also try to avoid breathing with your mouth open (if you are not talking/singing of course!) as it dries out the mouth/throat.
Best of luck xx