The above makes it look like you have a granny flat in your rucksack and you have a low opinion of her. For shame!
Heeheehee
I have a canvas bag in the style of a holdall but smaller. It's a little shy of eighteen inches in length and it holds cables, tuner, strings, a mains extension reel, some switch cleaner and nail clippers. I don't gig but if I did I imagine I'd have to be a lot more focussed about what gets carried in it than I am now.
I'd consider a rucksack if I didn't already have a gig bag for my bass to put on my back. Although I have a hard case for the bass, it's not used for the walk to my local because it spoils my gait and I get problems with my neck as a result. As I have a gig bag for the bass that can be worn with shoulder straps I'm happy enough to carry the bag. If I was going in a vehicle, the hard case would be used and then the rucksack would be ideal.
I suppose it is inevitable that I will get into pedals and other peripheral stuff which will make me rethink my luggage but I won't get a larger bag just now because I would tend to look for gear to fill it up.
We'll soon be able to buy robotic luggage that follows us whilst looking like something cute out of a Japanese cartoon. Won't that be great?