the 1/3 superfree was put in place to avoid overindulging in carbs and protein. This is how extra easy works, unlike green where you are limited on meats/fish etc and original where you are limited on carbs. With extra easy you can mix everything together, but of course within reason.
Advising you eat a 1/3 superfree with every meal helps to portion control so you don't have a plate full of just pasta and meat for instance. Although still free foods, it is the carbs and meat etc that have the higher calories etc compared to say fruit and vegetables which are superfree. So although slimming world is not a calorie controlled diet, if you eat over the amount of calories your body needs in a day which is likely if you are not consuming your 1/3 superfree, then the result will unfortunately be no weight loss or even a gain in some cases.
Like avisk, I look at what superfree stuff I have first and then think what I can make with it. Curries, spag bol, shepherds pie, stews, casseroles etc, you name it can be filled with superfree vegetables. Frozen bags of unstarchy vegetables are also a good suggestion for when you need something quick. Superfree soup is also another good one to make.
Of course there will be some times when you may find it hard to include superfree into your meal and this is fine occasionally I think, as long as you are getting plenty of superfree foods into your other meals of the day
I often see suggestions that if you can't add a 1/3 superfree to your meal then have a bowl of fruit etc afterwards. I disagree with this. The reason being is you will likely be full after your meal and will therefore be eating more food just for the sake of it. This is a bad habit to get into, as one of the things we all need to recognise is when we are no longer hungry.