To save you money and time, simply make a copy of all your key on a copy machine, black and white and file it in your documents.
In case of losing the keys, just bring the key copies that you made on the page to your nearest locksmith and he will know, in most cases, how to obtain a new key for you in minimum cost, without having him to come to your home (so you don't need to pay any service call or rekey and or changing your locks ;).