Sack it off
Definition 1 of 1
Pro Tip 1/3Casual Tone
Used in informal situations, often among friends or in casual conversations, not in professional settings. 
The weather's rubbish, so let's sack it off and stay home.
Pro Tip 2/3Not Serious
Implies a laid-back attitude, suggesting the plan or activity isn't too important or can be easily rescheduled. 
This project isn't due till next week, shall we just sack it off for now?
Pro Tip 3/3British Slang
Specific to British English, may not be understood by speakers of other dialects of English. 
The pub quiz was fun initially, but it's gotten a bit dull lately. Fancy sacking it off?