When you are in a grassy area Not te ype of grass whr pokmon are found but wen the grnd is green.
wen the gound is green you should see fnky lines of differnt sades, there will be times when you will see a DARK line one that should stand up more than the rest that is where you will find an item, just wak over to it and push A
you can test this on Victory road if you didn't get the items, or on the islands

I found stuff on both Victory road and the islands