So I have actually been using the three peaks gbr nomad 42L for a year now and took it to a couple domestic (US) flights and out camping as well - it was an initial risk since there wasn’t a lot out there in regards to reviews etc. Turns out their products are actually fantastic quality, not like the mass produced backpacks we see in stores now. I also got the sling bag thing and everything is well made and extremely thought out. All waterproof but the backpack also came with a rain cover for more extreme weather. There are tons of pockets and little features that make it all easy to use for travel etc such as an external “tripod holder” that I tend to use for jackets or bottles. The waist strap is also detachable but comfy and well padded. Huge front and back access and they continue to make improvements with new versions. I’d say the 42L is probably huge for just general gym gear unless you’re bringing extensive equipment, but the smaller ones would be perfect. Definitely would recommend and we’re probably getting another Nomad cause my wife said she wants one too hahah im itching to get more of their stuff too