COMP1917 - not really. there will be notes on the web, which may be excellent or brief depending on which lecturer you get. the textbook will help you if you want to read ahead and be prepared for next weeks work or if you want to review something in more detail. if you are new to programming you really need to keep up and the textbook can help you revise or explain the same concept you learnt in lectures in a different way which you might understand more clearly. ultimately this one is up to you but if you really want to do well you might want to get it, if you are happy with a 51/100 then maybe not buy the textbook
MATH1081 - there is a small $15 textbook by Daoud and some other guy. you need it for one of the five chapters as it contains the homework questions. not absolutely essential but again you should get it if you are aiming for high marks. if you are content with a pass, then you dont have to buy it. (there is another textbook, a huge textbook that costs heaps that you should only buy if you are struggling and need help. you can borrow it from the library though (many copies on the shelves) so its not worth buying)
MATH1131 - textbook is not required. there are course notes though which cost 30/40 bucks which you really should get which includes notes on every topic + questions + some answers + past papers with worked solutions + information book. thats not required either but you would need to do a lot of mooching off friends to do well in the course.
this will be explained in your first few lectures though incase no one has told you