Our veg box gets delivered on a Wednesday so I always sit down on a Monday evening once the kids have gone to bed with an armful of my favourite recipe books, a pad and pen and my laptop.
Firstly I log into both my veg box scheme and my online supermarket simultaneously. I then check the contents of my veg box for the week and opt out of any items I don't want or adjust my order size according to the weeks plans and what nights I need to cook. I write down what's in my box and get looking through my recipe books. I plan to use the most perishable items first and literally pick recipes which feature one or more of the box contents. I think it does help being a vegetarian as you are used to wanting the veg to be star of the show.
I check the ingredients list and add anything I need to my supermarket order. Strike through the veg you've used and move on in the same way. As long as you've picked the right size box for your needs you should be able to find a use for it all in a week.
I then add any other bits I need onto my supermarket shop and set this for delivery the same day as the veg box. I'm really aware that this sounds like a total faff however now its become a habit it takes on average 30-40 minutes and means I rarely have to make extra trips to the shops. Each day I know what we will be having to eat and can often get veg prepped during the day if I have any spare time rather than a frantic hour before dinner when I'd much rather be spending time with the kids.
I guarantee this approach will save you time and money!