I assume you know how to repair a puncture, but a couple of tips. Center the label on the tire next to the valve, it makes it easier to match the position of the puncture on the tube to the tire, so you can check whether the culprit sharp object is still embedded.

Never use the tire levers to refit the tire, use your fingers, or you risk a 'snakebite' puncture if the tire traps the tube. If you can't get the last bit on, the trick is to make sure the rest of the tire is sitting as far down into the rim as it will go. There is a lot of friction between the rubber and metal so you may have to work your way round the wheel several times squeezing the tire and pushing it right down into the rim (you can use soapy water as a lubricant if all else fails).

We had one puncture in Denmark and none in the Netherlands.

You need a bicycle lock, although we try never to leave our bikes unattended. One of us guards the bikes while the other does the shopping. If we have to eat inside a restaurant we lock the bikes and make sure we sit where we can see them. We always make sure the accommodation has secure storage, unless it is somewhere obviously safe.