I never load more than three rounds in the tube these days; and if I were to carry a couple extra rounds when stand hunting, they stay in my vest pocket so they can be accessed quickly. I've found those leather and elastic butt cover things with cartridge loops annoying, so you won't find one in my pile of hunting stuff; and I also despise rifle slings with cartridge loops. In all honesty I don't remember the last time I had to shoot more than once (the reason I only load 3 rounds), but there have been times when I did use those extra rounds; as on several occasions I've dropped three deer from a group, and on two occasions I could have dropped a 4th (I wanted to, but was reminded of the processing bill; so bit my trigger finger!). But for anyone feeling the need to carry multiple rounds, the best thing I ever found I got at Wal Mart. It is a small canvas cartridge wallet in Realtree camo; it has loops for ten rounds, closes with a Velcro tab, holds all rounds noiselessly, and easily fits inside a coat pocket. I never carry it anymore, as it is not necessary for the little day hunts I do; but it does stay in the vehicle with a few extra rounds "just in case".
One thing I really like about the fact that Marlin levers utilize a loading tube is the ability to keep/store 2-3 rounds in the tube, as in the tube they are always handy in a pinch; and provided you don't forget your gun, will salvage a hunting trip when the stresses of life cause you to forget to load your ammo stash with the rest of your gear. I remember going deer hunting early one frosty morning years ago with my BIL; and after a couple of hours drive he realized, as we gathered our gear to trek to the stand, that he had forgotten his box of Coreloks. I thought that was real funny until I drove 75 miles one morning; then realized, when I reached behind the seat to get my 30/06, that I had left my gun standing by the carport door!