I ought to be the expert here as my ex-husband not only had a Masters and a Phd in being frugal but he wrote all the text books!!!!! Unfortunately I rebelled once we separated and went the other way

TRAVEL - When you stay in a hotel remove the soaps etc immediately you get to your room, then the maid will think that she forgot to give you any and will give you more. Help yourself to teas, coffees etc everytime that you walk past the trolley - take them home with you.
ENVELOPES should always be re-used.
STAMPS - this tip is for those who write to a family member frequently. Use the smallest denomination of stamp possible then get the recipient to return them to you when they reply to your letters, sell the used stamps - he used to buy halfpenny stamps and sell them for one penny each used!!
NEWSPAPERS - shred and soak to make paper logs to burn in winter.
TREES - those that blow down in storms should be chopped up and burned as fuel with the paper logs.
FALLEN FRUIT - place on garden wall with a tub for the money - passers by will purchase them. For larger quantities advertise them for sale in local newspaper. Only advertise one year, keep names of those who responded then contact them in future years to see if they would like some more apples.
UNDERPANTS - get wife to patch them when they go into holes
SOCKS 1 - get wife to darn when they go into holes.
SOCKS 2 - when you go to the launderette and find an odd sock remaining in the washing machine from the last person who used it, don't throw it in the corner with the other odd socks ... go to the corner and have a look for one of a similar colour, it doesn't have to match. Take them both home.
DRIVING - remove shoes to get a better feel for the controls. Do not stop at junctions, just keep moving slowly so as to conserve fuel.
ICED LOLLIES - when on holiday make your two children share one iced lolly or ice cream. Limit their drinks to one each in a restaurant.
You want more?
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From over the pond....