The worst thing about I-49 is that lack of stops along the way. You can go a long way without any place to stop. I think between Alexandria and Natchitoches there is abolutely zero stops. And between Natchotoches and Shreveport, there isn't much either. Shreveport is about exit 202. Alex is about exit 80. Natchitoches is about halfway between. As you get closer to Lafayette, there are more exits.
There is an exit at Alex that has a McDonalds, Burger King, Texaco (with excellent BBQ inside), La Quinta, so that would be my exit of choice. Once you actually get into Alex, there isn't really much close to the interstate. You have to drive into town.