I don't own a working vehicle and must hike five miles into town to get my mail... and then turn around and hike back home while carrying it all. It is to my advantage to have the best carry bags that I can get.
I've been experimentally buying messenger bags, duffle bags, and backpacks to see which ones I like best. I want to share the items that have become my favorites (so far). Note that I am not associated with the sellers of any of the items shown here. This post more like a review; it is not a commercial advertisement.
CROSS BODY BAGS, subtype MESSENGER BAGS
Favorite: Lifewit 17.3" Messenger Shoulder Bag for Men
https://www.ebay.com/itm/Lifewit-15-6-17-3-Laptop-Messenger-Shoulder-Bag-Men-s-17-3-Coffee/333213905...
Pros: Among the highest volume capacity in a messenger bag. Leather and metal buckle straps. Full metal zipper closure for main compartment. Made of canvas, which I prefer to leather. Lining of bag is of a material superior to polyester in quality. Wide strap that comes complete with an effective leather shoulder pad.
Cons: Leather straps are fiddlesome to unbuckle on the move; not a biggie though, as you can always stop walking for a few seconds.
Runner-Up: Ahmik Men's Vintage Canvas Cross-Body Bag Messenger Bag
https://www.ebay.com/itm/Men-Vintage-Canvas-Cross-Body-Bag-Messenger-Shoulder-Travel-Bags-School-Sat...
Pros: High volume capacity. Canvas construction, including straps. Unlined interior is well-organized. Six-hooks used for flap straps.
Cons: No shoulder pad.
Runner-Up: Rapiddominance Classic Military Messenger Bag
https://www.ebay.com/itm/Rapid-dominance-Classic-Military-Messenger-Canvas-Shoulder-Laptop-Bag-Bags/...
Pros: High volume capacity. Canvas construction, including strap.
Cons: No shoulder pad. Over-flap is a bit too long. Lining is polyester and is best removed. Interior is unfinished (strings at the stitching seams).
CROSS BODY BAGS, subtype DUFFLE BAGS
Favorite: Plambag Canvas Duffle Bag
https://www.ebay.com/itm/New-Plambag-50L-Large-Canvas-Duffle-Bag-Travel-Bag-Duffel-Overnight-Weekend...
Pros: Large enough in compact configuration (about three times what a messenger bag will hold). Expandable by unzipping two end zippers for even more room. Canvas construction. Fairly roomy additional end compartments, and a frontal compartment.
Cons: The shoulder pad that comes with the bag isn't cushiony enough and should be replaced by a better pad.
Runner-Up: Cotton Canvas Duffle Shoulder Bag (either military surplus or made to look like military surplus)
https://www.ebay.com/itm/Cotton-Canvas-Travel-Equipment-Flight-Carry-Duffle-Shoulder-Bag-Small-or-La...
Pros: A good basic duffle bag, without the Plambag's styling and compartmentalization. The large one has actual duffle bag level volume capacity. The smaller version is still about 50% larger than any of the large messenger bags mentioned above.
BACKPACKS
Favorite: Hynes Eagle 40L Backpack
https://www.ebay.com/itm/Hynes-Eagle-40L-Trave-Flight-Approved-Carry-on-Backpack-With-Packing-Cube-B...
Pros: Holds enough, usually, though I doubt that it has so much as 40 liters capacity. It's in the same volume capacity range as a medium duffle bag. Polyester construction is okay for exterior, even if it would make for a lousy lining.
Cons: None noticed, other than the advertised capacity might be higher than the actual capacity. This kind of puffery appears to be very common in sales of bags and packs.
No Runners-Up yet. I bought a Hynes Eagle 44L Backpack, which was a disappointment. The 40L is better.
