Hey Rcramere,
This question often pops up from time to time, there are a lot of people who start out on the DL end of the spectrum and then migrate over to the AB side later on, there are also some members who Identify as 50/50 splits, 50% AB and 50%DL. I'd say that I am dominantly an AB, and it is not really a fetish for me but a lifestyle, a state of being and part of who I am, so I think I'm experienced enough to help a baby out
First off, as far as essentials are concerned, you'll definitely be wanting some diapers, if you don't have any already. I'm assuming you have some on hand being a DL and all. Premium medical or AB brand diapers are always the way to go. As far as other essentials, if you are looking to baby out, I'd pick up a stuffed animal, a pacifier, baby wipes, a bottle, a rattle and maybe some baby food or baby like snacks, at least these are items that always make their way into my regression time. Depending on where you shop around you can get some of these items for cheap.
With regards to how you go about regressing or exploring your AB side, that's something that I don't think anyone can answer. All AB's are different you see and everyone regresses in a different way. What works for me might not work for you. Also it's not as simple as acting like a baby or watching/playing with childish things, it's often some combination of the two and being an AB doesn't always mean regressing exclusively to baby age, your little side could have a variety of baby ages or distinct baby behaviours that it enjoys.
I can suggest some things that might guide you in your regression better. For instance, try diapering up and surrounding yourself with baby items and do what comes naturally. Perhaps you can think of some things you liked to do as a toddler or a small child and perform those tasks while diapered. There really is no right or wrong way to regress, so diaper up, think of what makes you feel little and go with the flow, you'll figure out.
For me regression has always come naturally, so it's very hard to outline what makes me regress and like I said what works for me might not work for you, my baby behaviours might not be your baby behaviours. I think the difficulty a lot of DL's who try exploring AB have is that they overthink it because regression isn't as natural an inclination for them. Your best bet is to either try some of what I suggested or to simply diaper up and do your own thing, find your own way.
Good luck to you and happy regressing