For her birthday, I made my sister a travel tote that would:
a. Fit her ginormous camera with its ginormous lens plus an extra lens that’s also ginormous
b. Fit all her necessary travel documents and stuff aside from the camera
c. Be presentable when going out to restaurants and the like
d. Survive the rigors of travel!
I measured the base to fit her camera’s bag insert exactly, with allowance for her to be able to put her water bottle, umbrella, travel documents, etc. I also tried a varied construction wherein the body is a single piece with 2 side panels, instead of my preferred usual construction of 2 faces and 1 long gusset. This provided the bag a more rectangular base (less curved) to fit the camera more snugly. I used the gemini strap adjustment (which my sister likes), making the straps long enough to not hit the elbows when putting the bag on the shoulder (an important detail for us), and then just for a little added security, a last minute bag flap (which ultimately wasn’t really necessary but was a nice feature to have). Finished with contrast pink and purple stitches, and brass bag feet.
She used this on our 3-week Europe trip last March/April, and it fit everything really nicely. The bag is a tad large (she knocked a few people around with it haha), but perfect for the size of the camera (Canon 6D + 24-70mmL lens + 16-35mmL lens) and everything else she needed to bring. It wasn’t an issue in museums (I think they more vehemently go after backpacks than shoulder bags), or even in fancy restaurants (Michelin approved!). It got knocked around, placed on the ground, brought to the zoo, rained on, etc., and has proven to be a great mix of being practical whilst not looking too rugged/sporty for the fancier places.