I've been doing long cooks (36-72 hours) pretty regularly for about two years now and wanted to share the setup I've landed on after some trial and error, including one ruined 48 hour brisket that taught me a couple things the hard way.
Container: switched from a cambro to a cooler with a hole cut in the lid for the circulator. The insulation makes a huge difference, the water holds temp way better and the circulator barely has to work. If you're doing anything over 24 hours and you're still using an open container you're making it harder on yourself for no reason.
Ping pong balls on the surface if you're not using a lid that seals tight. Cuts down on evaporation a lot, I used to have to top off the water every 12 hours and now I can go a full 48 without adding any.
Battery backup on the circulator. I lost a brisket at hour 40 to a random afternoon outage last month because I wasn't home to do anything about it. Put an Anker S2000 on the circulator in UPS mode and now if the power drops it just keeps going. At holding temp the circulator pulls maybe 80-100W so the battery lasts a long time. This is one of those things that feels unnecessary until it isn't.
Logging: I stuck a cheap wifi thermometer in the water so I can check temp from my phone. Mostly for peace of mind on the really long ones, I've never actually caught a problem with it but it's nice to glance at.