Surely he should be having a snack every time after nursery? To be fair, fuck knows because I don’t have kids, but when I worked in EYFS pretty much every child had some form of snack shoved in their hand as soon as they met their parent. Some of my kids still get collected by a parent who is opening Tupperware to get a snack out for them as they approach! I only say this as you say “he will expect it every time” - even if it’s just raisins, surely that’s what most parents do?
He sounds exhausted. He’s having that “safe place meltdown” thing where they hold it in all day at nursery and then it all comes out with you because you are their safe place. I used to see my reception kids leave and utterly crumble as soon as they got to mum and dad - throwing their coat on the floor, crying, refusing to carry their bookbag etc. It made me think what the fuck are we doing to them to make them that tired and crabby at first 😂
Shove a snack at him every time straight out the door, and probably some water/squash or something too. Ignore the tantrum while it is happening - literally just stand there on your phone or something and don’t give him any eye contact. It sounds horrible but there’s nothing you can do in the moment - trying to sooth them etc can a) make them worse/more overwhelmed and b) give them what they crave, so they then tantrum more to get it. Choice based language - “if you choose to scream because XYZ you will be choosing not to go to the park. It’s up to you.” “Yes, we can go to the park because you made such a good choice to be sensible when we came out of nursery!” It gives them a sense of autonomy and control whilst also ensuring that they know that no park or whatever it is is a consequence for their own actions. Also the classic “you’re showing me you are not ready to walk home, so we are going to wait here until you can.” Incredibly calm, measured tone of voice.
I’m not saying you can’t talk to him about the tantrums at all, but in the moment they cannot be reasoned with. You could approach it with him in the evening when he’s calm and say that you really would love to be able to take him to the park on set days, but at the moment his behaviour is showing you he’s not ready for that. Say that you know because he’s such a good boy that he will be able to show you he is ready for the park tomorrow, and you’ll know he’s ready because he will have calm/kind hands and a sensible voice or whatever. When he meets you after nursery reinforce that again.
That’s what I suggest from several years of work in EYFS including with multiple children who used to throw themselves on the floor and scream and scream whenever they were asked to do anything. I became immune to it over the years but it nearly broke me at first so god knows how you manage when it’s your own child!!!