You need to remember,,,
#1. YOU divorced your husband, your son did NOT divorce his dad.
#2. When your son is with his dad, it is his time, and his father does not have to check with you with what he does with his son, as long as his son is safe, you have no business needing to know what he does with his son!!
#3. Your son is not a baby, he is 9 years old, and yes that is still young, but he speaks clearly, and is old enough to let you know if something was wrong during his visits with his dad.
#4. Any gifts that are given to your son, through friends of his dads, should be no concern of yours, most likely he is probably hiding it so it won't hurt you?? You may want to suggest to his dad if any future gifts, maybe just have them stay at his dads, so your son doesn't feel the need to hide them??
I'm not being snooty here, I too divorced 7 1/2 years ago, and worried the same as you. I have 2 beautiful daughters now ages 21 and 17,,, my youngest is graduating H.S. this June,,, My youngest daughter was a year older than your son now,,, she was 10 years old,,, and even though they both loved both their parents, and their dad also was careless during our marriage when it came to our daughters, along with divorce years, I had NO control what he did when he had them, but I sure was ready IF they ever got hurt, (god forbid) I was ready to let him have it!!! I eventually learned, they needed their time with their father, and when he had them, I just moved on to MOMS time out, and eventually learned not to worry about them, they were old enough to let me know if something happened, and as for what they did, or with whom, I divorced him, I had no control what he did with our daughters, and if I was so concerned of sharing my daughters with their father who didn't think safety my way, I should of stayed married to him till they were grown,,, NEVER could I do that, so I just had to think my daughters were old enough to know right from wrong, and know they were okay when they were with their dad!!!
And now, I pat myself on the back for the way I raised my girls, they are GREAT girls, with good morals, they are well manered, and I have NEVER had to worry about them doing the wrong thing, I raised them well, and I'm so VERY PROUD of them!!!
So just remember, you have sole custody, and he will be with you a good part of his life, so teach him all the rights and wrongs, and as fast as the years go by, (and that they go by QUICKLY) Don't stress, just ENJOY him for who he is, and what he becomes because YOU will be the number one who shows him all the good ways in life!!! Gifts aren't what molds your son, it will be what comes from the heart, NOT the pocket book!!! So give him the peaceful times with his dad, but remember, YOU will be the one he looks up to, and cherrishs year after year while he grows up and becomes that man!!!