When I am travelling overseas I normally have a couple of packets of tissues like these in my pockets.
Or they are in a day pack if I am off for a swim.
If you have been caught short in a squat toilet with no paper you will understand their importance.
Where To Get Them
You will find that you can buy packets fairly easy in most countries.
Often, in Asia, you will find some old poor people going round selling them so why not help them out and buy a couple of packets?
In Hong Kong you will often find you get a packet, with your change, in a convenience store.