Are there any good radiation measurement devices to recommend to bring along when traveling to places that have radiation level that is not suitable for a 8 hour or longer stay?
A Geiger Counter measures the current radiation level. It can really only tell you "It's safe here", "don't stay here too long" or "get out of here, NOW!". If you're going to stay in an area where the length of your stay could expose you to a dangerous total amount of radiation, you need a Dosimeter (The Wikipedia page links to a list that compares specific models).
But any area where you could receive a dangerous amount of radiation over the course of as little as 8 hours is almost certainly not accessible to the public.
Well, the obvious is a Geiger Counter. It's simple to use - with usually a counter on the screen indicating the radiation, and beeps to provide an auditory cue as well.
When I went to Chernobyl, we were provided with one upon entry. They're lightweight, handheld and immediately clear on how to use.
They're often called Radiation Detectors as well, especially for marketing purposes. Indeed, a search on Amazon's website for either will show you can buy consumer-grade devices from around $150 and up, depending on the features and quality.