To acclimate your cat or dog to its carrier and so they'll have something good associated with it, feed them in their carrier. That way, it will not only be easier to take them to the vet, but if there's ever an emergency, it won't be hard to get them in it. Also, if you make the same sound each time you feed them, and you need them to come in an emergency, you can make that "time for food" sound and they'll come running!
This is a page about homemade pet carrier ideas. Buying one or more pet carriers can get quite expensive.