TL;DR: Less is more sometimes.
I'm a pretty keen photographer but I also prefer to travel with carry-on only. This forces some compromises in both photo gear and clothing but I have it pretty well sorted now after several longer trips. Here is my progression over the past 10yrs or so:
Started with a Nikon D40 6mp DSLR with the kit zoom 18-55mm in a small size shoulder bag. Being my first DSLR I had nothing to compare it to - so it n that regard it fit the bill and got the job done. Kit zoom little lacking on the ultra wide angle end.
Next trip I had upgraded to a Nikon D90 together with a Sigma 10-22 ultra wide zoon, a 50mm 1.4 prime and an 18-200 zoom. I reluctantly dragged this around in a Think Tank Urban Disguise 50 shoulder bag, which looks like an oversize laptop bag.
This was too big to fit into my 37L backpack, so had to be carried separately. The bag itself weighed 1.5kg empty and could swallow a massive amount of gear. This can be temptingly dangerous as you add more and more gear to the bag in order to "fill" it. Add the above gear plus filters, batteries etc and it was around 3-4kg - which got really tiresome, really quick when walking up to 10km a day around cities.
(Not my image) Photo credit:
The Phoblographer - The Psychology of Photography
For my next trip, I'd upgraded to a Nikon full frame D700 SLR and I also took a 16-35 wide zoom, a 50mm 1.4 and an 85mm 1.4. I'd also brought a new backpack, the F-Stop Loka, seen below.
This bag includes the option of a padded internal camera/lens storage unit. I did not use one on myself, electing to wrap my lenses in t-shirts and packing a small, soft, crushable Domke canvas bag in top which I used once at my destination.
This bag was weather resistant, had a wide flat strap which made carry more comfortable - although there's no getting around the fact that carrying a full frame kit around isn't going to be that light - particularly if you were like me and were infatuated with using fast prime lenses.
A couple of trips in 2013, including backpacking/hiking in New Zealand - I took nothing but a Fuji X100s and a Go Pro. I didn't feel that restricted and boy was it liberating to not carry a bag around everywhere.
Fast forward to 2014 - and while I still had a full frame Nikon kit - I now also had a micro 4/3 kit - much smaller weight and size. I used my same carry on size F Stop Loka backpack, in which I put this small shoulder bag - a Lowepro Event Messenger 100
This bag was able to fit my Olympus OMD EM-1, a Samyang 7.5mm fisheye, 9-18mm zoom, 25, 45 and 75 primes - and still didn't feel that heavy.
For my upcoming trip in a few weeks - there will be a mix of hiking, travelling by train and car. From my past trips, I came to the conclusion that I didn't like having to carry a bag around all the time, no matter the size. As a result of this - I decided to purchase a pocketable camera that still packs a punch, the Ricoh GR. This will be my walk around camera, always there, no bag required, weighs 246grams and has a very sharp 28mm equivalent fixed lens with an APS-C sensor.
I will still take my Nikon SLR with a light weight 18-35 zoom for the landscape shots that I like to take - this will be wrapped in a t-shirt and in my backpack together with my tripod during transit. This usually lives on the back seat of the rental car while we are driving around. I have moved away from taking a multitude of fast primes for travel photography. While they certainly provide a distinct look with shallow depth of field - I found found that shallow depth of field normally blurs away any kind of context in the photos - and for me, travel photos are all about context. I want to be able to visualize the whole scene. This also forces me to focus more on good composition rather than rely on smooth blurry bokeh to create interesting photos.
Sorry for rambling on a bit. In summary - I've moved away from camera specific bags as I find them overpadded, oversized and heavier than they need to be. Cameras are so good these days that a pocket camera IQ is more than what most people will need. If you still want to take a DSLR, wrap it in your clothes
