Acc to me , it mainly depends on the course you are taking ,
Like
For btech, you can revise some of mathematics chap that you know would be used in ur future course like trignometry I guess (as I have heard my friends talking ) .
For mbbs, you can revise some of the units like human physiology, human health and diseases and reproduction.
For bcom., Idk really bt may be some accounts and economics
For bba , you can also go through some some basic mathematics of 7th and 8th class I guess like profit and loss , simple and compund interest. Etc.