It should be lightweight, but large enough to hold a good amount of your favorite beverage. I personally prefer a 24oz bottle, so I know it will last the entire night. Your individual needs may vary.
It should be easy to carry, either clipping onto your bag, or easily fit into your bag. When investigating, you want to keep both hands free for tools, holding railings to get up stairs, or lights. You lose a lot of ability when you have to carry a water bottle in one hand.
Your chosen bottle should keep your beverages hot or cold for an extended period of time. This usually means purchasing an insulated metal bottle or tumbler. Each manufacturer should include the time limits on the label. Expect timing to be off, but not absurdly so. Things will remain colder far longer than they will remain hot.
My favorite bottles come from Simple Modern. I left my bottle in the car on the beach in 96 degree weather. With all the windows rolled up, you can imagine how hot the car was. When I returned and we got the AC going, I took a tentative sip, only to realize there was still ice in the bottle, and my water was cold. I’ve been a fan every since.
I usually purchased the Wave bottles, but those have been phased out. I’m now using these, which look and function basically the same. I can verify that if I fill my bottle up in the morning, but drink other things and don’t get around to drinking what’s in the bottle, it’s still been cold the next morning.
You can also check out the Simple Modern website to see different styles of bottles and tumblers they make, as well as take advantage of any sales they’re currently offering.