Here is my personal experience (when traveling) :
I carry 1 luggage that goes under (of course).
I also use a small sling bag (Pacsafe) to carry wallet, glasses, etc...
As for my gear, I always carry (carry-on) a full backpack (Lowepro, Trekker 220, not sure of model)
without any problem so far, of about 10kg (22 lbs) of :
- K-5ii + grip
- another body K10D + grip or K-01 (lighter)
- Theta SC (360°)
- 4-5 lenses (from Pentax 10-17 fisheyes to Sigma 120-400)
- AA batteries, recharge cables, extra SD cards, grey card...
- small flash
- rocket blower, etc, etc, etc.
I traveled multiple times (from Canada) to USA, Caribbean, 3 times in Europe (cruises).
Never had any issues.
No issues at all to cross some borders (to get on cruise ships), then travel “lighter” on each excursions
.
Hope you will have the same kind of experience..