Uniforms: Most airlines will pay for your uniforms, however some airlines might expect you to cover the cost of the uniform, which will be deducted from your salary in small monthly instalments.
Commissions: Some (low cost) airlines will pay attractive commissions for any food & beverage or duty free products you sell in-flight. This is an added bonus that motivates crew to sell more, a win-win situation for both the cabin crew and the airline.
Languages: If you are considering applying for a European airline, it is good to know that most major carriers (Lufthansa, KLM, Swissair, etc.) require that you speak the national language of the airline and that you are a legal resident of the country the airline is based in.
Airlines in the Middle East require the applicants to have a strong knowledge of English, while any additional language is considered an advantage.
Furthermore, airlines in the Middle East sometimes offer a separate allowance if you can speak other languages besides English. In addition, you might get assigned to operate flights as a “language speaker” to the country whose language you speak (e.g. if you speak Italian, you will likely go to Italy quite often).