Body... Bicycling Accessories 101

Here is my list of items for beginning bicyclists (once you have a good bike!), in my order of priority. Remember, you usually don't get more out of something than you invest into it! (But you also don't have to buy all of this stuff at once -- I would consider down through #9 to be the most critical initially, especially if you consider riding alone more than a mile from your house -- forget going anywhere without a helmet and some bright clothing.)

1) helmet (make sure is well-vented, fits well to protect both forehead and back of head, and is ASTM or Snell rated)
2) "High-Viz" (Lime green) shirt, vest, jersey, and/or jacket, preferably with some reflective trim or details (Be Seen!)
3) gloves (fingerless are probably best for road, full-fingered for mtb)
4) water bottle cage (preferably 2) and water-bottles (at least 16 ounces each, preferably with auto squeeze-valve, such as Nike and Camelback running/cycling bottles have)
5) padded shorts -- try to get breathable fabric, good chamois pad, and leg-hems rather than "grippers" -- I haven't had very good luck with "gel" pads, and rubber leg-grippers make a lot of people break out (or at least itch) once they start sweating, especially in direct sunlight
6) rear "blinky light" (red, flashing) -- a good bright one, such as Blackburn or Trek, for riding at dusk or in foggy/misty conditions (you never know when you might need it, to be seen)
7) "frame-pump" air-pump with mount (to mount between water-botle cage and frame) -- make sure nozzle will work on at Presta valves (WITHOUT an adapter), preferably both Presta and Shrader ("regular" US car-style valves)

8) seat-bag (for mounting under saddle with velcro straps) -- Bell medium-size bag for approx. $8-$10 from Wal-Mart works well, but these can get as fancy as you want -- to hold following items ("8a" through "8g")
8a) spare tubes (Presta-valve 700x20-25c for road, 700 x 25-35c for touring, 26x1.9-2.2 for 26" mtn, 29x1.9-2.3" (equiv to 700 x 50-55c) for 29er -- Presta valves are always best, but make sure you have at least one pump to match) -- approx. $2.75 each at CoolByke in Hannibal
8b) tire-levers
8c) tube patch-kit WITH glue (the glueless patches DO NOT work, especially for road-tubes)
8d) allen-wrench tool or set, or (better yet) bicycle multi-tool with allen-wrenches, screwdrivers, and chain-tool
8e) chain tool, if not included with multi-tool above (at least get the $3 model from WalMart, which will work a few times before it breaks)
8f) emergency poncho or stuffable rain-jacket
8g) replacement "quick-link" chain-link -- SRAM and others sell them for a couple bucks each

9) glasses (for eye protection, from sun, radiation, debris, pavement, deer antlers, etc.) -- clear ones for night and early morning (small safety-glasses work fine, and are widely available for around $5), good medium-tint UV blocking for day-- I prefer the auto-darkening glasses from Optic Nerve, Performance, Nashbar, etc. -- these will run $30 to $200 (or more!), but good optics are worth it, and the better the features and clarity the higher the price
10) breathable cycling jersey, with zip-front (full front-zip is best) and rear pockets -- "HIGH VIZ" (lime green) is by far best color
11) energy bars, drinks, and/or gels (you'll need to average at least two per hour on all rides more than 2 hours long) -- Cliff bars are by far the best, and a box of 6 can be had from WalMart for less than $6; GU energy gel is the best, and can be a get-home saver if your muscles start cramping; Gatorade still works fine as an energy drink, though we have to re-condition ourselves to not be afraid of calories while we're riding -- glucose syrup works best, but regular processed sugar (sucrose) is still better than artificial sweeteners
12) water-resistant helmet-cover
13) cycle computer (includes speed and distance)
14) helmet-mount light (WalMart has some strap-headlights that will let you be seen and at least see your computer and shifters; the best light systems can run as much as $400 or more, though prices are falling as LED and battery technology continues to improve) -- a light is necessary for others to see you, but a really bright light is critical for you to see the road or trail if riding before dawn or after dusk
15) white "steady" handlebar-mount headlight, preferably LED with 3-4 AA's, such as Cateye EL500, but almost any steady white LED light will at least let you be seen after dark (to truly see the road or trail with it you probably need at least 1 Watt, or 60 Lumens)
16) tools (Park tools are the best, though Nashbar and PricePoint both sell a "home" tool kit for around $45 - $60 (depending on sale price at the time) that works fairly well for a lot of things)
17) work-stand
18) enough grease, lubes, and small parts to cover most situations (note: it's important to learn which types to properly use where -- using something that "works" can cause catastrophes later)