Cash equivalents 2 years before and in retirement

I'm a bit confused about the information on cash equivalents. (Outside of say 60% stocks/40% bonds) Some say keep 3-5% in cash equivalents while others say keep less because of opportunity lost. What do you all suggest/what do you do? I feel comfortable with 3 years cash, but not sure if that's the smartest course. (SS covers half my expenses)