Must Have Beginner Slr User Lense Canon SLR Camera Musts?

SLR Camera musts? - must have beginner slr user lense canon

I bought a new Canon XSI. What are some of the musts for a beginner SLR camera? I have a 18-55mm. What filters and cohorts? I know nothing of cameras, if you now the reasons for his choice could, I appreciate it:) Thanks!