Just realized I never talked about these. I think these are a gods-end for the urban cyclist. They're panniers that can be converted into a backpack. Pictured here is an Ortlieb Vario PS, but other brands make them - some better than others.
I think they're king for urban cyclists with lots of stops as you can convert them in give or take 3 seconds from one to the other (if you've not bought garbage) and have so much more comfortable carrying capacity compared to classic pannier with a single strap and you can take your valuables with you.
an alternative is open-top cargo panniers like the Green Guru FreeRider or the Air Pannier that let you just throw any bag into them. They're expensive for what they are but seem like an easy concept to DIY. The downside is that they're designed to leave on the bike which isn't safe for a lot of places.
Honestly if I were just going "throw anything into it" I'd just go standard issue bicycle milk crate or cage or similar, seems much less a hassle.
uhh why not both? It's nice to have the extra capacity.
running both a rear rack crate and panniers of any kind that are easily removable is a huge ergonomical hassle at best
I agree, but the ones I mention stay on your bike and only the contents get removed so the capacity is just available when needed...well, until they get snatched which has happened to a few of my crates