Try having a look at a military grab bag. Usually a decent size for stowing away, modular so you can add small pouches if required and very hard wearing. Example below
https://www.military1st.co.uk/f56930a236onesz-propper-bail-out-bag-coyote.html?___store=default&refSrc=133164&nosto=productpage-nosto-1
LZ