I was reading another thread about an answer to switching purses - and I have another answer. It is a pattern that I have been using called the Smart Handbag. The Grace Smart bag pattern has a removable cover to slip over the bottom of the complete bag. It has a zippered closing to keep everything safe and pockets in the lining.
Here is a picture of my basic black bag with a cover I made for Halloween.
Here is the link where I got the pattern http://thesmarthandbag.com/