Essentially you don't really need much for the camera to make something 'cinematic', that said there are hundreds of accessories available to assist in film making with DSLRs.
The most common items people tend to buy are rigs that allow you to stabilise the camera for shooting handheld. More importantly though, these tend to offer focus pulling systems and given that to use a DSLR for filming 'cinematically' involves using manual focus, having something that allows you to focus smoothly and accurately can help. Another important item is having a decent recording system for audio, as relying on standard camera audio isn't going to cut it.
What tends to make something 'cinematic' really though is down to the lighting, if you can light a scene properly, that will go miles towards giving you a better look. The final aspect that gives a film that 'cinematic' feel is the grade, it doesn't have to be something so stylised that its obvious, but just matching colour grades from shot to shot goes a long way to helping keep the suspension of disbelief.
You would end up spending a fair bit of money on lighting, audio and rigs, so to do things cheap, you would probably be better seeing how you go and you can use cheaper lights such as work lights to light a scene.