You can now find 1.5V Li-on AA batteries with, and that's a game changer, built-in charger and a type-C port!
I have one in my wireless mouse. If it dies, I change it to a spare and charge it right from my laptop (and the battery that was empty becomes the spare)
You can get them with different voltage drop-off curves
E.g., this battery is 1.5V for ~70% of the capacity, before it gradually reduce to 1.0 V
https://www.xtar.cc/product/xtar-1-5v-aa-clr-3300-lithium-ba...
edit: And one with USB-C and linearly decreasing voltage curve https://www.xtar.cc/product/xtar-aa-lithium-lr-2000mah-usb-c...
Came here to post this. I'm 100% agreed with Mr. Geerling.
For a fun challenge try to find a non-built-in-battery arc lighter (eg: candles, grills, etc). When I found one I bought four (think camping/disaster bag... if everything is AA/AAA then having a shelf-stable fire starter is easier/safer than lighter fluid).
For a fun sidebar check out the "Panasonic BQ-CC87AKBBA" which is effectively a combo "in/out" battery charger OR USB battery pack(!). It'll suck in (unfortunately) Micro-USB and charge your AA's, then switch a button and it'll spit that power back out as a battery bank. When I find one like that for USB-C, it's going on my christmas list.
Look up plastic battery holders that hold 8-10 along with a 4x charger and I just swap batteries out and recharge them into that buffer/holding cell. I'll have to look into the Eneloops as I've been working with the Amazon Basics and generally have 1-2 batteries fail out every few months (and am specifically looking for heat-resistant / outdoor applications).
Last one: Lots of cheap solar products have cheap rechargeable AA batteries inside... you can generally open them up and swap the battery out if they're not working any more (and/or potentially scavenge the charging panel if you think about it!).
The NITECORE UM10 is an "in/out" charger too - it handles various sized LiIon batteries one-at-a-time. A switch on the end determines if it is charging or discharging. Their site says it's discontinued, but I thought I recently saw them at a shop in Seattle. Time to pick up a spare.
I had this charger once! Really cool with the powerbank option. Although, these days, 5V@1A with no PD is probably something to use maybe in emergency, it's too slow for modern devices.
I haven't used them, but IIRC they maintain a constant voltage until they're discharged, when it instantly drops to 0. That may be a problem, because if your device has any battery indicator, it will show the battery as full until the end. Nothing will tell you that you need to replace the battery before the device powers off. That's why I decided not to buy them. My mouse knows when my alkaline AA battery is low and gives me a warning.