Some low priced information
Your 18-55mm lens takes a 58mm filter while your 70-300mm takes a 62mm filter. You can get by with using a single filter by purchasing a 62mm filter and a 62-58mm step up ring that will allow the 62mm filter to be used on the 18-55mm.
Step up rings can be had as low as $4.49 on eBay. This is quite a saving over a separate 58mm filter.
This is the most economical way to do this however, it does get to be somewhat of a pain when switching lenses because it involves an additional step of switching filters.
The question of using a clear or UV filter over your lens for protection has advocates on both sides. One group says that any filter will degrade the imagery and that you should not use a filter to protect your lens. The other group states that a small amount of image quality fall-off is a decent price to pay for protecting your lens.
If you decide on a protection filter, make sure it is the best you can afford. Inferior filters (unfortunately Canon is among that group) will degrade your imagery. Excellent filters are expensive but those such as B&W and Hoya Multi-coated are worth the money.
Besides the possibility of using a protective filter; a circular polarizer (CPL) is a great investment and will pay dividends in better photos. Again, buy the best you can afford. If you get your filter from Hong Kong, you will usually save money. On eBay, new 62mm CPL filters run anywhere from $10 to $90 and, there is really that much difference in the quality. The CPL is really the only filter a beginner needs. It is one of the few filters the effects of which cannot be duplicated in post processing.
As far as lens hoods, I recommend that you ALWAYS USE ONE whether you are shooting outdoors or indoors. Most lens suppliers except Canon regularly supply lens hoods with their lenses. Canon only supplies hoods for a few lenses, mostly the "L" grade models and expects you to buy their overpriced hoods. However, you do have a choice, China is producing some very adequate hoods and hoods for your kit lens are being sold as inexpensively as $10 on eBay. I use a Chinese hood for my 17-55mm f/2.8 IS lens and it works just fine.
Now about lens caps. The Canon OEM lens cap is a side pinch cap in which you need to squeeze the sides of the cap to attach and remove it. This is sometimes difficult when using a lens-hood. I recommend a center pinch cap and these are available on eBay sometimes for less that $5.00. I bought a used Canon 300mm f/4L IS lens which came with a cracked lens cap. I replaced that cap and five other side pinch Canon caps with Chinese made center pinch models for less than Canon charges for a single cap. The Chinese center pinch caps come with the Canon logo if you desire.
Now as for flash units. If you are on a tight budget; a used Canon 420EX flash is a very serviceable unit that can be obtained rather inexpensively on eBay. There are quite a few that are under $100 on eBay right now. The bidding will go up but, you should be able to obtain one of these units for right around $100. They don't have all the bells and whistles of the newer models but are very good units at an excellent price. Later on, if you want to upgrade to a 580EX, you can use the 420EX as a slave.
