It’s so simple. Throw in one column each day - or throw in the whole week’s worth on the same morning if you like - and just take where you’re delivering to each day. On Monday throw Saturday’s in as well.
Don’t ever feel guilty about leaving an empty column for the person covering your day off each week, because they’re only taking where they’re delivering to as well.
If it’s double slotted, and there’s only mail for one address, then write a number on the remaining leaflet.
By the end of Saturday’s round, virtually all of the junk has been delivered with a proper letter, and you haven’t wasted any time walking down countless paths all week just to deliver an item of unaddressed ‘mail’ that will almost certainly be thrown away, unread.
Astonished by how many people actually seem to struggle with stuff like this.