At this age, playing. Honestly, I don't think you need anything else. There is a window of opportunity for a particular kind of play, I think, up to the age of around seven, and kids need to go through this much more than they need to learn to read.
I don't mean I'd stop a child from learning to read or teach them if they requested it (providing other signs of readiness were there, like sign recognition), just that I would not push it on a child before seven. (maybe not even then-just that IME most kids are ready at seven for the beginnings of abstract work if thats what you want to do with them)
(random question here. I often see posters saying "my 4 yo is on a pre-K level with this " or a "2nd grade level on that". How do you know this stuff? I never have any idea what level my kids are at. For my 4 year old, I could say, "she really likes drawing and animals but has no idea how to spell", and thats about it. Even my 8 year old it would be, he's done a year of latin and two years of maths and knows basic arthimatic and the tables and likes algebra and probabilty more than geometry...I mean, how do you know what level your child is on? Genuine question.)
I go by the grade levels for the curriculum we're using for Math; the level of standardized test we do annually; and the grade level that I submit on our paperwork. I also know, from previous work experience, roughly what reading level DD is at.