I just wanted to pop on (as a lurker and former DBer) to offer my support. I think you are an incredibly patient man and she is crazy to be doing what she is doing.
Also...this business she pulls every time you pick up the kids, it has to stop. It's her little way of having 'control' and it's not right. The kids should be ready for when you arrive. Period. If there is stuff that should be packed, she should do it the night before. Remind her that she CHOSE to become a single parent, you did NOT...that means she needs to step up to the plate & cover the slack. I would truly say something to her like 'I don't appreciate the children never being ready or even close to organized when I pick them up. I did not CHOOSE to be a part time parent, you did. My time with them is more precious than ever now, and I find it disrespectful that my time w/them is being wasted when you should have had them prepared to go"...I don't know if you agree, but that would drive me BATTY! I am now divorced, DB could only go so far- but when we change off with the kids, I show my ex the respect I want in return and make sure I have everything organized so I'm not infringing on HIS time w/the kids. It's common courtesy and she seems to just expect you to wait around until she gets around to doing what should have already been done. If she wants out, she needs to realize that being a single parent means virtually NO time to yourself, trust me. She made this choice, she needs to live with the reality of it.
Again, sorry to butt in I think you are doing a great job!