Oh, FB.... that's awful... I really feel for you and DS.
It's very unfair on your DS not to be able to bring toys back and forth, but having to bring PJs and swim trunks.... If your ex wants to buy specific stuff for 'his' house, I would strongly suggest he gets his priorities right and buys his son pants / socks / PJs and makes him feel at home when he's there.
As a 'step-mum', I pride myself on my DH's kids feeling welcome here at any time. They both have their own rooms, and have their own stuff here. There is no stress on the kids to 'clear' the room (There is some stress on them to CLEAN their rooms - a different story!!!!!!!!)
It's always difficult to expect kids to leave stuff. 13YO SD is really good at bringing whatever she wants to wear, but the 10YO often goes back in all her 'good' stuff and then comes in her uniform again!!! So, yes, we do make her leave some stuff here, but we do explain why and it's only neccessary stuff....
Yes, as step parents it IS difficult because we pay maintenence and then have to fund kids stuff here / have a larger house to accomodate the kids etc., but sorry.... that's the score...
When DH and I agreed to have this baby (DS due in May - our first together), we were totally agreed that both of his kids will continue to have rooms at our place (yes, this means moving to a larger house). Nor will we attempt to reduce maintenence to his ex. Our decision to have a baby is not automatically her problem.........
Now, to be fair, we've been together for 10 years so the kids are second nature in our lives... When they were younger, we did get more stuff from their mum (they liked to bring teddys, juice cups etc) and when they first came to stay with us, we only had a two bed appartment, but EVERY week, without fail, we demolished 'our' apartment and created 'the kids' apartment before they arrived........ Elder SD STILL refers to 'her' room in the apartment... We've only recently told her that it was actually our room and we moved out of it when she came so that she felt more at home....
Same goes for holidays - We take the kids skiing, then we provide ski gear (to be fair, their mum did provide some bits she had, but we wouldn't expect her to go and buy this stuff). Conversely, if she goes on holiday, I don't expect a phone call looking for a handout (this HAS happened!!!)
Sorry, long ramble... But you are really NOT being unreasonable or petty. FFS - surely your Ex can provide toothpaste and towels????????
Do you have a CO? What does it say in that about these extras?
Feel for you!