Following is what I have used as expat living different countries and frequent traveler across primarily Asia and Europe but at times also worldwide. Always in black camera bags since black is discrete. I have had up to five camera systems as carry on. I never check in my gear.
1. Tenba PBP, Photo backpack (near 10 years old) – Fits plenty, low weight, durable and comfortable. It has weighed up around 18kg on international flights, including always large pro carbon Gitzo on side. It is rare for the pack to be weighed or even questioned at check in.
2. Tenba Large Messanger bag - Carries my 4x5 Shen-Hao and 17" MacBook Pro... it kind of slips along to enable carry more than in my PBP, sitting in small compartment on luggage car during check in... thus rarely gets noticed…
3. Stand straight in line and when arrive to counter, appear relaxed in spite of that weight on back... = avoid show weight
4. Appearance of routine traveler, well prepared with passport, tickets, friendly... making job simple and quick for staff...
5. Only one small and within limit checked luggage, sort of to compensate and make simple.
6. If need carry more, e.g. books (heavy) or other gear, simply in the smallest looking plastic shopping bag they fit. Such bags tend to not be considered by staff… and could even be from transit shopping somewhere…
7. Film – Uhhhg… this has caused worst argue over the years... it is simply difficult nowadays, and with lack of respect at x-ray especially in Scandinavia (Sweden, Finland), while in Asia hand inspection is not much issue.
8. Polite persistence and ask for supervisor and police if necessary. My gear is simply my private property which I am not willing to risk at security checks. However very happy to cooperate and show them all during a hand inspection after the x-ray per myself taking out item by item for their view.
9. If being questioned I explain that I travel frequent and have carried ALL my gear on ALL flights. The international practice is by all airlines for camera and laptop to be exempt from carry on restrictions. Not sure what is referred by “camera” in that context…. Besides, once they have begun issue your boarding pass, they are in practice obliged to let you board…
10. I do not fly KLM.
It feels good! I have now sold off gear to reduce, since I am tired of carrying and having much gear. It feels it has been in way of my photography, less and simple makes photography more a joy and more a focus on the image! However, with above list I qualify as perhaps among ones who have carried most as carry on.