Cfred had some very excellent advice and I agree with her on everything she had to say. DO NOT give in to tantrums...EVER! If you do it even once, you will be rewarded with many more tantrums since your son has figured out that they work to get what he wants and to get your attention. Giving choices works really well at this age as well, but make sure the choices are both equally okay options. For example, "Do you want milk or water?" instead of "What do you want?" or "Are you going to sit nicely in your seat or do we need to buckle you in to help you sit?" I do this with my own daughter who is almost three and sometimes has a hard time sittting still at the table (booster seat with buckles is a must!). Lots of positive reinforcement helps a lot as well. Praise him up and down when he does anything positive as he will want to do more of that to get that attention. And ignore the tantrums as Cfred said, or let him go have a rest in his bed to calm down if he is too worked up (I have done this with my kids and sometimes they will send themselves to bed to calm down now). Good luck! Stay calm, consistent and strong and this will pass.