Always carry a cord, keep a charger in your car, and plug it when when you can, I never have to worry about it dying. I also carry another battery for just in case I can't get anything else :-/ So I've never had a problem.
Even though I mentioned this in my other post I want to re-emphasize this.
Now I work at home, so I have a luxury that a lot of people do not have. However in my office sits my computer on my desk, and attached to it is my usb cable for my iphone. Probably 70% of the time when I come in here I will quickly plug my phone in, and then unplug it when I leave. This could be 5 minutes or 5 hours.
Also in the living room where I normally spend some free time and stuff, next to my chair, I have a power cord plugged into the wall. So when I am there and not actively using the phone, I just plug it in. I obviously leave it plugged in while I sleep as well.
Just these two minor things though, mean I almost never get even close to being low on battery, and I use my phone a lot. If I go out, the phone is most likely 90%-100% charged when I leave, so it is very easy to go away for several hours. As I mentioned I also have a battery back up in case of emergencies, but that is what it is for.. essentially if the power goes out for an extended period of time, I can keep charging the phone as long as I can come up with batteries.
I don't have a car charger right now, but it would be an easy addition and increase the time I could spend using the phone while going out, if that were ever a problem for me.
Now if someone works at McDonalds (not making fun), and does not want to leave their phone in the back un supervised plugged in, I can fully understand that. However if you do get some kind of locker or the such, might not hurt to keep a power cord in there so when you go on your break you charge it for 15 minutes. 15 minutes from a wall socket will provide you a good amount of charge to finish out the day.