Spending time doing pointless bullshit or being otherwise unproductive. Wastelanding is usually an enjoyable activity (such as watching TV or playing video games) but ultimately a complete waste of time and of existence. Also known as "wasting away".
Person 1: Hey Spencer, what have you been up to?
Person 2: d00d I got Madden '08 and I've just been at home wastelanding
Guys Spencer couldn't join us this evening as he is busy wasting away