A holdall is a large soft bag for carrying clothes. Pack a holdall, a canvas holdall, throw it in the holdall.
It is British, and America says duffel bag for much the same thing. The name is exactly what it does, and it is the standard bag for a weekend away because it takes an awkward shape without complaint.
1nounholdallA large soft bag for carrying clothes.
“He threw his gym kit into a holdall and headed out.”
holdall is a bag.
Also accepted in games: duffel bag
Hold plus all, a British compound naming the bag by what it does.
hold + all.
Etymology from Wiktionary, CC BY-SA