The majority of companies have some fast food or casual restaurants in their repertoire. It depends on the cuisine you seek. If it is Mexican food, I have recently seen a fast food version of that with Service Check and there is another company that has been discussed here on the forum that I don't remember right off which one it was because the client is not in my area. I noted the other day some Chinese posted on one of the major fast food shopping companies. I do barbecue through two different MSPs, and the list goes on and on. While many of the casual dining chains are currently not shopped, as the economy improves, I expect to see a number of them back.
Getting signed up with companies and seeing what they offer in your area is the key here because even when a particular company offers a particular client in my market, that client may be with a different company in your market. And keep in mind that there is a lot of competition for some fast food and casual dining shops, so you need to check the job boards fairly frequently. Some companies post throughout the month, but more of them post during the last week of the month for the following month and during the first week of the new month.