If you plan on flying to Europe and you don't know the baggage limits in advance, you could be in for a nasty (and expensive) surprise. If you then plan to fly within Europe itself, you'll get hit again, but even worse. Unless you are good at packing really light, get ready for some shockers. The overhead bag you use at home may not fit in the overhead. The extra laptop bag you're used to bringing on a U.S. domestic flight will get counted as a second bag. That wheelie suitcase you have may take up half the baggage weight limit when it's EMPTY!
Thankfully, the person who runs this All Cheap Flights site in the U.K. has provided us with links to the baggage limit pages for airlines in Europe. So you can go in there and see how badly you are going to get hit if you don't scale down what you are bringing. Plus as high as some of these charges are, you could buy a new ultra-light bag and pay less than you would for the extra fees on one or two flights.
Peruse this practical travel gear blog you are on now for ways to travel lighter with some and smarter, but here's one key piece of packing advice: almost anywhere in the world, you can pay someone to do laundry for a reasonable price. (As in don't hand it to the butler at the Four Seasons.) Here's another piece of packing advice: almost no trip requires more than three pairs of shoes---often two is enough---and one of those could be some light and versatile sneakers.