From a wide range of devices on the Android platform, you need to choose the one which is able to satisfy all requirements.
If possible it is preferable to buy or rent a device with support of mobile high-speed Internet 4G LTE — this will provide you with cheap and fast Internet. However, such connection is not available in all cities and countries.
For travel it is better to purchase devices with 2 SIM cards. In this case, the second SIM card can be changed to a local one in each visited country. However, you should remember that some tablet models do not have a telephone module and they are not able to make a call via the mobile network as the SIM card in such devices is only for the Internet.
Choosing a smartphone or tablet it is better to buy a device with 2 cameras — rear and front. The rear is for regular photos and the front for video calls and selfies.
Choose a device with built-in GPS module. It allows you to determine your location very accurately even when the Internet is not available.
Buy a case to protect your device from external influences. It is also good to choose a model with moisture protection, you never know when and where you will be exposed to rain …
Another very useful thing — Power bank which allows you to charge a smartphone or tablet when there is no electric network. There are various capacities, masses, brands and prices.