I am using all these with EE2.9 with basically no issues:
Cartthrob Order Manager
Ct Admin, User
The only one I am having issues with is Wygwam actually. I am finding some pages are CPU spiking and then timing out depending on the content in that field. I have to do some more testing and then will contact P & T about it, but if I remove the stashing of that field, the page loads quickly, add it back and it cpu spikes and never renders.
It's only on a few pages on the site, so it must be ?specific content related? - overall it's all working quite smoothly although I did need to attend to some session/login/forms/xid hash stuff as this all changed a bit after 2.8.1 - see
After upgrading to EE 2.9.0 my front-end login page no longer works
...and a few conditionals needed a bit of revising with the new conditionals parse, but all in all way less pain that I expected (2.7.2 -> 2.9 in my case)