A bonus by the end of the year is always nice. However, there is a far better way to keep your employees happy, that also pays off in the long run...
Dr. Marius Rietdijk studied in his thesis 'Influencing organizations' the way that behaviour within an organization can be influenced. Don't panic: there was no manipulation involved. The lack of complimenting employees stood out to him, however, and he decided to make a further inquiries into this phenomenon.
He concluded that complimenting at the moment itself is much more effective than a financial boost. This is simply because the reaction comes straight away then, and not months afterwards.
This can also prove effective on an event. By showing that 1 you have noticed their good action/good work and that 2 you show this to them, this will immediately create a boost. Those who take pride in their work, will continue with a smile. By giving well-founded compliments regularly, the conditioning takes place immediately. Thus 'I have to' changes into 'I want to'.
It takes some practice, but it is definitely worth the effort. You should be extra conscious about everything that happens around you. Give well-founded personal compliments and you will soon see the positive change. Your team and event will improve, so what's not to like?