The phrase meaning do with whatever money or food you have left is one of those that is often misspelt (as in ‘tied over’) and therefore isn’t immediately recognisable as having nautical roots. Originally it referred to the practice of floating with the tide in the absence of wind to fill a ships sails. Making slow headway was better than none. Hence to ‘tide over’. The adoption of the phrase to mean coping with what you have is pretty logical when you think about it.