You don't specify scale, so I'm assuming 25mm/28mm or equivalent in this response,
For starters, there are diecast vehicles, like the venerable Matchbox Models of Yesteryear or Lledo if you can find them. Sometimes a visit to the toy section of the local thrift store can uncover a treasure trove of gaming supplies. Sometimes not, though - it can sometimes be a frustrating experience.
There are some WWII era transports that can be used, although some conversion might be necessary, as some trucks are too obviously military in appearance. Company B has Model T Fords available.
Blue Moon has a line (Highways and Byways) of suitable vehicles.