Ditto the motorola talk-about's. Simple, small and reliable, as long as you have line-of-sight up to 10 miles. If you have it on all day and use it enough you will get about a day on the batteries. In a diesel truck cab you must have the gain on high to hear it over the engine.
I bought seven of them 10 yrs. ago for each conductor on a 7 choir brass piece (performed outside) I composed so we could stay together. Only have two receivers left. We've used them on a lot of trips and they just keep disappearing.
The newer WalkieTalkies have more range, better reception and transmission range. Costco sometimes has some in stock.
regards, as always, jefe