Earlier on in this thread, OP, you asked if another poster had ever had a 'bolter', and you referred to your children as being 'difficult.' Knowing that this was the case, perhaps you should have taken reins with you, in case you couldn't get the trolleys that you needed.
Or have back carriers, as kungfupannda suggests.
Or get the bulky items, such as nappies, baby wipes, tinned goods, loo roll, washing powder etc delivered monthly so the weekly shop goes down to one trolleyful - and I have to say that even when I had three children aged 4 and under, I never had to use more than one trolley except at christmas.
You could have booked the online shop for first thing Saturday morning, got it all put away and then gone out to do something fun with your family. And if you book the slots well in advance, I doubt you'd have a problem getting the slot you want. You could book a late night slot on the Friday night - all the kids should be in bed, and you and dh could put the shopping away unhindered - and then the whole of saturday is yours!