I bought 2 cheap plastic baskets from Wilkinson - one is permanently in the sitting room and the other in the bedroom and each has a packet of nappies, pk of wipes, cotton wool, nappy sacks, baby powder and cream in it as well as a changing mat so that no matter where we are his stuff is there ready for a change.
I also have all of the above packed in his changing bag so we're ready to go out at a minutes notice.
I learnt the thing with the baskets from observing my sister - what NOT to do - whenever she'd change her LO she'd have to get my 9yr old nephew to run about the house fetchng wipes or nappies or whatever. I swore then that I wouldn't do this - apart from the fact that I'm pure lazy
it just makes better sense