Some helpful links I've collected over the years:

• https://www.quora.com/How-do-top-students-study
• https://www.reddit.com/r/cscareerquestions/comments/3jc9t5/cs_student_looking_for_ways_to_make_some_extra/
• https://imgur.com/gallery/pHUdq (Actual poor student cookbook)
• https://news.ycombinator.com/item?id=7673628 (A free cookbook for people living on $4/day)
• https://news.ycombinator.com/item?id=8181101 (The most common errors in undergraduate mathematics)
• http://mathoverflow.net/questions/13089/why-do-so-many-textbooks-have-so-much-technical-detail-and-so-little-enlightenme
• https://www.coursera.org/learn/learning-how-to-learn

If you do something related to computer science:

• https://news.ycombinator.com/item?id=8085148 (work on some side projects, for example program an economy simulator, invent a simple layout/markup language, implement a LISP-machine in C)
• Get familiar with the UNIX command line, learn VIM and use Spacemacs as editor. Use org-mode for notes and git/magit for version control of all your projects and notes. Make use of a cloud service to keep all your files accessible from all your devices.

As someone who has developed RSI during their studies: If you feel that you don't have enough time to exercise, ignore that voice in your head and get a minimum amount of 7 minutes intense workout and 1 hour of very light exercise (e.g. walking, cycling or swimming) each day (and consider two sessions of longer intense workout per week, e.g. 60 min. swimming lessons). After each hour of sitting do a 5 minute break to stretch or drink a tea (Awareness.app for OS X is a nice software solution that can help you with that). A bad physical condition will affect your mood and mental performance negatively.