Just like a bender, but the participant is sober. Usually sober benders are undertaken by regular drug users who have realized that they are showing signs of addiction. In such a situation, the individual may decided to spend a period of time going cold-turkey. In addition to going cold-turkey, sober benders involve the user also attending various club nights out, often more than they would have previously done while taking drugs.
Those who undertake sober benders often find they have an excess of money due to their zero consumption of alcohol or other substances. Hence they may go on more nights out, more expensive nights out, or spend shit-loads of money on vinyl.
Carl: What's wrong with you Harry, you love the white rocks?!
Harry: Not anymore Carl I'm on a sober bender.
Sam: I went sober-bender once. I quite enjoyed it. Then I did loads of coke and died.