My theory is that Trevor is stomping Johnny in trailer 2. Ash is the biker chick, watching helplessly as this happens. Perhaps Johnny gets pulled into drugs with Ash after the LC chapter was destroyed. He does this because his life is now pointless, and he decides to go nomad, and takes Ash with him out onto the road. During their journey, Ash gets Johnny hooked on meth... and he doesn't care, because he feels he has no purpose anymore. They eventually arrive in Blaine County (a meth riddled place) and probably owe Trevor money or something... which is why he is beating Johnny up. Perhaps Johnny's "Los Santos" patch is an easter egg?
Just a theory I wanted to share!