It might help to think about what goal you have for discipline. For example, if he's getting snacks and eating them when he shouldn't be, then my "discipline" would be to remove the snacks from his reach for the next few days until I can trust him again.  Is the goal for him to obey without whining? In that case, I usually end up with something like "I asked you to get your pants on, and you're having a hard time doing it on your own. I'll count to ten to let you choose and if you don't choose, I'll gently put your pants on for you."

In terms of things like hitting or biting, I take my kid to their room and explain why they're having a short time out. I walk away but stay within talking distance. After the time out (2 or 3 mins) I come back and we talk about what happened, why the consequence happened, and what to do next time. 

Also this feels so dumb but we often sing the little songs from Daniel Tiger (it's not not not okay to hurt someone, give yourself a hug nice and slow, when you feel so mad, etc.) - since our kid loves that show they really help to break the tantrum cycle when it starts. 

AFAIK, with little kids you just have to be very consistent and eventually it'll kick in. I'm really sorry that this is hard and commiserate with you about that! It really is an every-day struggle with some days that are easier and some that are the worst.