I second the Trent 1100 battery pack. I picked it up for a month long trip to Europe and it worked perfectly. I would charge it overnight as needed and for the iphone it was easier to recharge it in my backpack while I was out sightseeing. I have recommended it to several people who have also had great results.

Fully charged it can charge an iPad once or an iPhone up to 6 times. It takes about 9-10 hours to charge the iPad which I found to be about the same speed it discharged in use (ie the battery charge stayed the same if charging while in use or slowly charged if not in use). It seemed to charge the iPhone 4 faster than being plugged into a wall socket.

It has a USB connection so you can plug anything that charges via USB into it. It's packaged with a self-coiling cord and several dongles for most types of USB connections (micro, mini, etc). You need your own Apple USB cable, though.

Also, a quick note on the open apps. I don't believe they are using battery power, just memory space. iOS saves what you were last doing in them so you can reopen to the same spot. You need to check Settings/Options to see what apps are allowed to provide notifications and other battery eaters.