HPost #25 by Peter Bodtke contains an excellent summary
May I expand a bit on several of his points and several other
posts which followed.
# 3 . The bank machines can be very capricious , depends much on the quality of the computer link to their main servers , be prepared to be denied service at any time . Going to multiple different banks the same day is often futile since all are operating from the same network, wait a day and try again.Best to not wait until all your cash is used up before topping
up.
# 8 there are indeed some big modern PEMEX stations which advertise that payment by credit card is possible ' but I always pay cash too everywhere
An other possible way to economize at hotels is to ask if they have a price
" Sin factura" . This is a tax dodge used at some hotels in Mexico where they
will rent you the room at pre-tax rate if you will pay cash and forgo having a paper receipt issued.

# 6 actively use your change ALL the time even when you are in
your home country . Nothing is sillier than somebody who whines about
the weight of coins in his pocket or is too vain to use " small change"

The Euro notes may not be refused in European countries that use them
but private businesses in any other country are free to reject anything they
please.If they do take them as a courtesy they are free to charge whatever
fee they want so don't complain about being ripped off.
Stick to going through bank machines to get the cash you need.If you bring wads of
exotic paper money you will have to exchange them at exhorbitantly high service fees
and often long annoying waits at local banks. The same holds for travelers cheques which are
now holdovers from a bygone era.

Don't give away foreign currency without explaining to the recipient
that it is real and what it is worth in his home currency.I stayed in a hotel in Esquintla ,GT and got into a long conversation with the clerk.He had a funny story , a few years before a European guest was checking out and asked for help to haul his stuff , a lot of it,down to the taxi.Then as a tip he handed the clerk a colorful item of paper money which the latter had never seen before.The clerk told me that he thought is was some cheap foreign store coupon or worthless play money . Feeling somewhat taken advantage of he said he crumpled it up and tossed it in the garbage. Only later did he learn about Euros and recognized that what he had been given was a really big denomination Euro note equal to several weeks of his regular pay . Now he laughed about it , buts what a shock it must have been.doh