This post is addressed to the Asterix and Obelix camera users...the photographers who are going to carry next to nothing or nearly everything.
I make no judgments - I have been in both categories in my time and benefitted and suffered in equal amounts. Some shoots needed one shot with one camera and some needed five hundred with five. The trick was to predict which scenario would play out and provide myself with the gear appropriate to the occasion.
The big ones seen here will suit the pro or am going out with a number of bodies, a number of lenses, and a number of accessories. The backpacks are proof against the vilest of weather and the roll-around can resist many, if not all, indignities in the cargo hold of an aircraft. They mean that whoever has hauled them to the job will have a studio-worth of choice to work with.
There is a price to pay. They are big. Loaded with gear, they are heavy. Assess the condition of your back and knee joints before you go...because you'll know where they are after you come back...
The little bags are for compact cameras - in one instance for the tiniest pocket cameras and in the other case for the slightly larger style with bigger sensors that is becoming popular now.
You might wonder at the idea of a case for a pocket camera - surely a pocket is the place...well, pockets are full of lint, and keys, and coins, so you need a protector even there.
Can you do a good job with a small camera? You know you can - and the craftiest ones of you out there will know when to opt for just that level of gear. Just don't tell the client that you did it easily - they might begrudge your fee.