They don't call it a "Classic" by chance. You can throw all you kit in these duffels, roll 'em up, click the buckles and go literally anywhere; from deserts (or the beach) to base camps, jungles to safari tours.
The 40 Litre capacity is great for long weekends or carrying all your sports kit, wet-suits, etc. There is a handy internal wet / dry pocket to separate smelly gear.
The welded seams make this bag 100% waterproof and very hardwearing. You seal it by pinching the top closed and rolling it down three to four times tightly before securing with the buckle at each end. Note, it can be tricky to get a really tight seal, so worth practising before you put the bag through its paces.