i carry slinkies cut and ready to use, but a friend of mine carries a 2-3 footer and cuts what he needs on the river. you already should carry small scissors for yarn, all you would need to do is carry a lighter to seal the ends (i don't smoke and i think its quicker to have them pre-cut, even if i carry more weight because of it)

as far as stuffing them, i use the .270 ball and just fill them by hand. after the end frays a little, heat it up and seal around the edge to make it into a funnel. i will stuff maybe 20-30" and leave about 6" unfilled. then just cut and seal into the lengths you want. it takes no more than 30 minutes start to finish and makes more slinkies than i can lose in a long weekend.

also keep in mind when you pull on the cord it constricts and tightens around the shot...push the cord along with the shot and this will open up the cord and the shot will slide right down.