Cycling, more than many other sports, is equipment-centric. I am of the minimalist school - you do not need a host of fancy gear to get started. Add those later.
What's the minimum gear needed? Here's my list:
- Helmet. Do not ever ride without one. It can mean the difference between a bad headache and being a vegetable. Make sure it fits well (see this guide for tips on that, along with other equipment needed to get started).
- Water bottle. Get one with a cage that attaches to your bike. Regular bottles do not fit in this cage, btw. An alternative is a hydration backpack. You really only need hydration tools once you start cycling beyond an hour, but it's good to have just in case.
- Pump. A portable pump that you attach to the bike is necessary, in case you get a flat or a slow leak. You do not want to be walking your bike back home. A floor pump is good to have at home, too, for easier pumping, but is not absolutely necessary.
- Repair kit. A simple repair kit would include a patch kit, a spare inner tube, 2 tire levers, a multi-tool for bikes, all in a small bag that attaches to the bike.
Other stuff you could get later:
- Gloves. I actually have a pair of these, and you could consider them essential. They absorb shock from the handles (cycling gloves are padded), but more importantly, if you crash, your palms are protected.
- Bike computer. This attaches to the bike (no, they do not have it in Linux or Mac flavors) and tells you how far you've gone, how fast you're going, your RPMs, and all other kinds of good info. Very useful, but not absolutely necessary. I do not have one at this point, but it's on my to-buy list.
- Gel-padded seat. For beginners, riding on a hard seat cycling can be very uncomfortable. This gel padding has saved me a bit of pain. Experienced riders tell me that you get used to it after awhile, and I have, to some degree.
- Glasses. To some, these are a must. I have not gotten them yet, but they block bugs and other debris from hitting you in the eyes. Has not been a problem for me yet, but then I do not go that fast!
- Shoes / pedals. The most efficient way of peddling is if you are using your up-stroke as well, not just your down-stroke (pulling the pedals up and pushing them down). To do this, of course, you need either cage pedals to put your shoes in, or the kind of pedals that lock into your cycling shoes. So You'd need special shoes for that, of course. I plan to get these some time, but have not gotten to it yet.
- Lights. These are a must if you ride when it begins to get dark. I do not do that out of safety concerns.
- Racks. Important if you want to transport anything. There are all kinds of racks and panniers (cycling bags). Awesome for touring or commuting.