I have had a few students from the lower years email me and ask me a few questions on how they can improve their CV and get an overall better chance of getting a placement after their second year of study, here's a few tips I've picked up while on my placement year and wish I started during my summer holidays.
I'd recommend making a Github account and start working on open source projects, if you're interested in any sort of development, web, programming, or scripting. You can create your own projects or find an interesting project and start contributing to it, don' be afraid to commit something, you're only learning after all. Any hey, github even offer students a free micro account, which means you can work on private projects, which would be great for University projects EDU.
Now that you've started your journey of creating a repo or have started to write some code for someone else's project, you're going to get stuck when it comes to coding, StackOverflow is a great resource, if you have any questions or are looking for an answer, this is the place to do it. Be sure to supply a lot of information in your questioning, and supply code examples where possible, because you don't want to be downvoted to oblivion, anyone from reddit should know this ;).
Trello has hands down been a life saver for me, I've been working on multiple projects at work and you can't remember everything, it's got a great UI and if you start to work on projects with other students, you can assign them tasks to do, check it out here.
These are a few sites I use and would recommend if you're interested in security, they have some great knowledge, tutorials and vulnerable machines you can download and own.
SecurityTube, Vivek has some great tutorials and all the content there is solid, easy to understand and great for someone who wants to get into security concepts.
VulnHub This site has some great vulnable labs, just download one give it a go, if you get stuck they have some walk through's you can take a look at to understand what's going on.
OWASP You can't get any better when it comes to OWASP, their mission is to make software security visible, and boy do they make it visible. I'd highly recommend looking at the OWASP TOP 10, projects, and cheat sheets.
Programming, Web, & Math
If you're interested in getting your math, programming, or web knowledge these are some great sites where you can sign up, and view your progress:
ProjectEuler is a series of math problems that you need to solve through programming
These are the main principles I've learnt from my year placement, and it you start to realize that you make a lot of code smells, and it is good to keep on top of your code by using some of these principles.
Hopefully this has been helpful to some people, I know it's quite overwhelming to start something, but hopefully you might get some use from some of these websites. If you have any good resources to add to this list, drop me a tweet
Now that you've had a taste of what you can achieve over your summer, why don't you join me at Leeds Hack in August, let's make something, and you can put your new found skills into practice, get your ticket here