1) UV Filters - a lifesaver - really and truly it's not worth not having one!
2) LCD Screen Protector - great for putting on the display on your camera to protect it from scratches.
3) Lens Hood - Useful in the sunshine but also as added protection for your lens!
4) Lens caps - I don't take my own advice, but really lens caps are great, use them!
I work with a Sony D-SLR A57. It has lots of bits and pieces that require the odd bit of upkeep here and there (don't we all!) but nothing too complicated. The biggest concern for most is cleaning those dust specks out of the camera sensor. Firstly, check the in-camera cleaning function. Lots have them and it often solves the problem. Anything a bit more complicated that involves digging around inside the camera and touching lots of shiny reflective bits..should be left to the professionals unless you're really confident.
This lens pen is pretty nifty, it's only a few pounds (in the UK) and has two functions. One end is marketed as a specialist non-liquid type cleaning element..basically it's a non-magnetic magnet type thing! You can use the brush to...brush, and the other end to pick up the fine dust specks. I use this for both the lens on my camera, and for the visual parts of the sensor. Gently!
Be careful when using a brush type cleaner - if you go too cheap or too rough, the bristles tend to fall off in the most awkward places. You want something sturdy that's not going to let you down!
These non-abrasive wipes are fantastic. They are lint free and ultra soft! It says so on the packet! But truly they are great, and they work really well with the lens cleaner listed below too. You can use the wipes on their own or with the liquid to get a better result. Ridiculously, the wipes only seem to be available at the moment as part of a really-expensive-set but it's worth keeping an eye out, they last a while too.
You can generally find a good lens cleaner on amazon, this particular one though I found by fluke. It was given to me for cleaning discs and actually it works really well, if not better, on camera lens's. It's not as good on UV filters, for some reason, so it's worth avoiding it or polishing it off them very well afterwards.
I've had the same cleaning cloths for years. I've not even properly 'cleaned' them. It sounds awful but actually they are really substantial and don't need much care. These are both for micro-fibre lens and work fantastically for rubbing off finger prints, small bits of dust and fluff and drying raindrops!
It doesn't take much to keep your camera up to scratch, if you're noticing specks that just won't go away then pop to your local camera shop and see if they offer a cleaning service. As a rule, I generally get mine cleaned once a year in order to ensure everything's working okay but sometimes you might find you come away with more specks than you arrived with - always check the cleaning system they have in place. If it's cheap, it's not worth it!