Cats are infamous for messing things around. Sometimes they deliberately keep on knocking thing over and there can be one of these three reasons why your cat is showing such behaviour:

1.Cat shows this behaviour when they are hungry. Make sure to feed your cat fresh food and water on fixed time intervals daily. If your cat remember it's time for food it will be less likely to knock over your items.

2.Cat likes to knock things over to simply play with the item. And to get your attention. 

3.It can also be a possibility that your cat is agitated with something and will probably be over it soon enough.