A few thoughts on that...
- A smart phone does a great job of lumping together all of the functions of a number of devices in a light compact device.
- Some phones have replaceable batteries that are pretty light, small, and can be found cheaply if you don't buy from the phone manufacturer.
- Power wallets can be had pretty cheaply and will charge the phone several times on a charge.
- Smartphone battery life can very long if you use the phone in a way that maximizes it. Turn off the features you aren't using or better yet turn the phone off altogether except when using it. Definitely don't leave the cellular phone functions on in places where it will be searching for a signal, that kills batteries fast.
- You are on vacation, you don't need to be taking calls. Use the phone only for outgoing calls and keep them brief, keep the phone function off the rest of the time and the batteries will last FAR longer. Limit your calls to checking in with family once a day or even once every few days. Better yet check in with an email or text message most days
- If you don't want to spring for a phone plan, many smart phones can be used as a WiFi device, even making voice calls with Skype. This is true for both android and iPhone platforms. WiFi is getting more and more available so this option is getting more practical. Picking up a used smart phone cheap is pretty easy these days.