Used colloquially to describe having sexual intercourse with someone who is not a virgin, especially when they are in a relationship. The analogy refers to a loaf of bread; it is not readily apparent, once the end has been removed, exactly how many slices have been taken.('You never miss a slice from a cut
loaf' is also used.)
If you put all your eggs in one basket, you risk everything at once, instead of trying to spread the risk.
(This is often used as a negative imperative- 'Don't put all your eggs in one basket'. 'Have your eggs in one basket' is also used.)
Boardinghouse reach is the ability to reach a long distance across a table to get food. We've used it in our family for as long as I can remember, when you reach across someone's plate, "Pardon my boardinghouse reach".