what is...
 

a Sag stop?

On organized group rides, a sag stop is a rest stop where there are snacks and drinks. That's it.

A sag wagon, is a support vehicle that offers mechanical assistance or a ride back to base camp if you're spent!

L8R

Support and gear. If its an actual stop, you can expect food, water, and some type of mechanical support.

Another term you will hear often is Sag waggon. Rather then a stop, its a car that provides all of the above.

thanks.