One of the hardest parts is getting coax that won't have too much loss on GMRS and still keep it light weight. A lot will depend on how high you are planning on getting your antenna up in the air and also what type of antenna being used. Using a sturdy mast will allow you to use heavier coax. Some of the cheaper telescoping masts are thin and won't support the weight. Go with the lightest coax with the least amount of loss that is acceptable to you.
I actually have a couple of clothe roll up j pole antennas made with faraday cloth. One is for 2m and the other is for 70cm. The 2m j pole works fine for both 2m and 70cm with a SWR of 18 or less. And the 70cm j pole works fine for GMRS with a SWR of 1.7 or less. I am using 30ft of LMR400 equivalent coax along with a Sotabeams 7m/21 ft telescoping fiberglass mast. I hang the clothe j pole from the top of the mast and run the coax down, attaching it with velcro straps to keep things from flopping around in the wind. 30 feet lets me get 9 feet away from the mast.
I normally will use some type of stand or 3 guy ropes on the bottom section of the mast to hold it upright on calm days. I will add three more guy ropes towards the top on windy days. I also have throw line and throw bags incase I want to just hang either antenna up in a tree.
I can throw my dual band or GMRS radio into my go kit along side my G90 HF radio for any type of portable use. I am also setup for sending emails with Winlink on HF and VHF if needed. My go kit is one of the Hart rolling tool boxes from Walmart. I have a couple of 50 AH batteries in the bottom case and everything else (besides telescoping masts, fits inside the other cases.
I can also throw a radio or two, some throw line, and the clothe/wire antennas and 1 or 2 10 AH batteries into a backpack and go light.