There is always someone worse off than you.

This is a saying which is often used to comfort people.  It can apply to health or possessions.

Getting off to a good start
is an idiom.  A related saying is well begun is half done.    A healthy pregnancy gets a child off to a good start.

Rattle it off means do a job quickly.

Dash something off could apply to a hastily written letter or nowadays, email.  Dash means rush or hurry as well as being punctuation.

To swank something off means to show it off.  It could be a garment being worn.

As easy as falling off a log (backwards) is a simile, which hardly needs any explanation. 

If you do something off your own bat you have used your initiative.  It is a reference to hitting the ball yourself in a sports match, such as a doubles game in tennis.

Spin off has various meaningsA spin-off is an invention which has resulted incidentally from a project.

Go off at a tangent means digress.  A tangent in geometry is a line which touches a circle or curve.  The metaphor is that instead of remaining on one path a completely different one is followed.

Knock the spots off means defeat convincingly.  In the Dictionary of Modern Phrase Graeme Donald gives the practice in dominoes and some card games of taking the remaining points from the loser’s hand and adding them to the winner’s score as the most likely derivation.

A camel might be living off its hump.  People temporarily without income, might live off whatever they have managed to put by for a rainy day.

Wipe the dust of your feet/shake the dust off your sandals is what Jesus’ disciples were told to do when He sent them out to towns and villages if they were not welcomed or listened to.  Matthew 10:1-16