From my experience you need to plan from the very start about not including anything you don’t need. Even if stuff isn’t used it still ends up packaged.
Also are you baking any lightmaps (using static/stationary lights and “building” the level?) because those can be VERY big
If you package the game WITHOUT the .pak function, it’ll package everything as individual files and then you can use something like windirstat (or even just windows explorer) to go through and see what files are making that size. You might find they are massive lightmaps - in which case either use lower lightmap resolutions or not baked lighting - or perhaps they are content you’re not even using. Or if you’re unlucky it’s just a lot of little things adding up to a big number.
Good luck