It's difficult, but you just have to do what you can to manage your own eating, and don't fall into the trap of keeping up with others who eat more, or following what restaurants/shops etc tell us is a portion size.
I hadn't really thought about this until I read Paul McKenna's 'I can make you thin' some years ago. Now a lot of it is irritating nonsense designed to make half a page of simple rules into a whole book, but the key point that stood out for me was 'eat when you are hungry and stop when you are full', plus eating slowly and mindfully so you actually notice this, so not eating while watching TV, phone scrolling etc.
Now I'd never thought about it before, but when I tried it, it was obvious and a really easy way to cut down at least a couple of hundred calories a day, which for a lot of us, will be enough to keep our weight stable and stop the gradual creep upwards.
Obvious things to put this into practice would be any type of eating out, because for many places, even a starter and a main is probably far more than many people want, but they eat it because it's there.
I'm quite good at avoiding this because I won't order a starter unless I either really want one, or I'm with a group and everyone is having one and I don't want to sit without food while everyone is eating.
But if I'm honest, if I've had a starter, I'm usually full when I've barely touched my main (I like to eat more earlier in the day, so can't do the common 'eat barely anything all day in anticipation of a big dinner' because I just feel ill if I do this) so I'll probably choose and eat my main with the intention of taking most of it home with me to eat for the next day. So I'll eat anything like salad, that won't save, and take away the rest. Or I might just leave what I don't want. Food is no less wasted if you eat it when you are full/don't want to continue than if it goes in the bin.
At home, make sure you serve yourself the right amount of food for you. Leftovers can always be saved for another day. I see endless comments on here along the lines of 'I'd just have soup/wouldn't bother with dinner but DH expects a big meal' as if people are obliged to provide food to other's preferences not their own. If you don't want a big evening meal, don't have one.
Either have a small bit, and have the rest for lunch the next day, which is what I often do, or make something light. If others in the house want big meals, they can make them. But don't fall into the trap of 'I'm not that hungry so I'll just have a sandwich/some picky bits' because often 'just' a sandwich or some picky bits will have more calories than a small cooked meal with meat/fish/other protein and vegetables or salad.