For comprehension, I used random passages from books, newspapers and poems. Tested Dd by discussing them. We also tried some of the past papers from private schools available on this website. For vocabulary, the CGP books were very useful. Bought the 9-10, 10-11 and parents guide verbal reasoning and comprehension books. Also the one with 2 practice papers.
For Maths, we did lvl 6 SAT papers and I set some questions involving multiple operations or steps.
NVR we used Bonds.
Didn't buy any books except for CGP. Got a couple of Bonds and Letts books from friends for timed practice papers.
Although not conventional prep ( we started only in June, but did one hour every day until the exam day), we found that this was sufficient. On hindsight, we could have spent more time on vocabulary, as that was what Dd found difficult during the exam.
Hope this is useful. All the best!