Bring two flashlights. The combination can be variable; what matters here is that one light is a good multipurpose flashlight that can show you the way to the bathroom at night when you are forced through circumstances beyond your control to walk/run/flail to the potty in brisk fashion, while the other is used for reading. I use a Mini-Maglite as my multipurpose light (uses 2 AA batteries), and a collapsible lantern light for reading (uses 4 AA batteries). The lantern light is great because it collapses into a multipurpose flashlight if you need it in a pinch, and then can pop back up into lantern mode for reading. It gives a warm, diffuse light which is great for reading at night (not harsh). Some people prefer to use a caver’s headlamp as a substitute for one of these choices, which is fine, just don’t look me in the eyes while you are using it (everyone hates that)!
As an archaeologist, it is good to pack your flashlight with you while in the field during the day for two main reasons:
1. At some point, you will find yourself in a cave, or in a hole, or under a car where you will really wish you had a flashlight, even in the day.
2. You might get lost and have to spend the night in the wilderness.
Expository Note of Truth – I almost never pack my flashlight during the day, because I do a lot of difficult hiking in the jungle, and backpack weight is a major concern. With that said, I have experienced both #1 and #2 above, and I really wished I had a flashlight during those times.
Awesome Pearl Of Archaeological Wisdom – Try to make it so that every tool requiring electricity you bring on a dig is either rechargeable or runs on AA batteries, and bring a massive pack of AA batteries with you on your trip (they will be used). Buying uncommon batteries in the third world (such as strange camera batteries or even D cells) will be expensive, and may be impossible.