Working to finance the holidays in Europe is one of options that the travelers always do. The best thing is that they can live for a while and know more about the country. Also, living in a non-English country gives you the opportunity to learn a second language and have lots of practice. I think it is the greatest advantage of have mixing work and travel.
If you plan to work legally in Europe, you need to do some researches. But most of travelers prefer to do casual illegal work such as working at ski or beach resorts, seasonal work as fruit picking and so on. But it would be risky that the wage is not enough to support your living for few weeks. Thus, you need to reserve sufficient money for purchasing a return air ticket.
There are some tips if you plan to work in ski or beach resorts. First of all, you have to find this kind of jobs before the season begins. Otherwise, these vacancies will be gone quickly. Second, you should not bring along with CV or job reference. Take British Immigration as an example, they may suspect anyone that will work illegally if they have these documents.
In fact, being a foreigner, it is quite difficult to find the causal work in Europe as unemployment rate is high in some countries. These casual seasonal jobs will be taken up quickly by other citizens in EU countries as EU citizens can work in any other EU countries. I strongly recommend that you must deeply consider your employment plan in your journey. You must have a flexible itinerary to seek work along your trip, only treating the causal job as a bonus to your travel.