I thought I was being clever

I pride myself on being well-organised and thought I had been even cleverer than usual when I pencilled in a date for a trip to the school uniform shop for one and only son's new uniform.
He is leaving his prep school and going on to secondary school in September.  His school had already broken up before others so I thought I'd take advantage of this and go to the uniform shop before it became a heaving mass of tetchy people trying on blazers.
I took out the list of uniform needed and blanched at the £14.95 for the ordinary, no-frills trousers.  Carefully I scrutinised the details - there was no special emblem required, so I made an instant decision.  ''We'll see what's in the supermarket,'' I said to one and only son.  
Our round trip began.  It was one of the hottest days of the year so far. In the supermarket we had the obligatory row about saying 'no' to the latest Playstation whatever gadget.  With a face full of thunder, one and only son stuck his head in the air and marched to the clothes section.  Here, after trying out seven pairs of black trousers, we found the right size and length.  They cost £5 each, so I left the store feelling smug that I'd saved £20 already.  
Then it was back to the car to set off for the uniform shop.  The traffic crawled along and we got hotter and hotter.  I couldn't remember exactly which street theshop was on, so that produced more tetchiness.  We eventually found the correct street.  Trying to park produced another sweat.  I looked forward to the cool interior of the uniform shop.  I pushed open the door and bumped straight into the queue.  It was heaving - I could taste the tetchiness in the air.  Why were these people here?  They were supposed to be at school. 
I joined the queue valiantly trying to remind myself of the £20 I had saved on the trousers in the supermarket.  I had earmarked exactly what was needed. I used the 15 minutes in the queue usefully to remind myself of the questions I needed to ask the assistant. Top tip:  ask them which items - craft aprons are a good example -  are a must-have and which are considered desirable.  Don't just automatically buy everything on the list.  Have you already got something similar at home which will be allowed by the school? 
The price of the blazer with badge already attached was reasonable enough.  But beware the P.E. kit.  That's where the 'how much?' bleep bleep moment hits you.  The reversible rugby/football shirt was £18.  The polo shirt was £6 - this is where I wished I'd got some from the supermarket.  I was too hot to criss-cross back there again, so I gave in to the feeling of 'Let's just get it now'.  With hindsight, I wish I hadn't.
Anyway, we were kitted out and made it to the pay desk.  I knew there would be an added extra.  I just didn't know where it would be.  It's like the shoe shop at the very end where they always try to sell you the cleaner to go with the shoes.  It's easy to get out of that one - just say you've already got it  - but the school uniform one isn't quite so easy.  You don't want your child to be the only one without that vital accessory that really nobody needed but everybody succumbed to.   Ah, here it was.  Did we want special printing of the school's emblem and one and only son's name on the way-too-expensive rugby/football shirt and the polo shirt. 
''Does everybody else usually have it done?'' I asked, knowing full well what the answer was going to be.
''Oh, yes,'' she said, immediately making me feel a skinflint. 
I couldn't bear him being the only one without it.
''Go on, then,'' I replied.  I shall just have to take comfort in the supermarket trousers.