When I worked for a family run coach company, the owner would often offer me a sweet from a tin of Setra kassbohrer travel sweets when we were working in the garage. I'm not sure if he bought them or if they were given to him when he bought the coaches.

I think you should have tried Opal fruits (or Starburst as they are called now). Who remembers the jingle "opal fruits, made to make your mouth water" ?

You can still get Smith Kendon travel sweets I believe, although I haven't seen them for ages.

I enjoy fruit pastilles. As also mentioned, American hard gums used to be great (I believe that James May sings the praises of these) but are hard (forgive the pun) to find. Sainsbury's own brand fruit pastilles are very nice, in my opinion, and have a texture that is firmer than normal for pastilles -- about halfway to an American hard gum and easily obtainable!

I prefer chewing gum (usually two pieces of Wrigley's Extra Peppermint). I seem to remember reading somewhere that gum chewing boosts concentration a little, and I believe it does help combat fatigue on longer trips.

I find it loses its flavour on the bedpost overnight, however :)