Water:
Everytime I go shopping I buy a gallon or two of bottled water and simply add it to my stock in the basement. I have probably arount 40 gallons there by now on shelves. Simple procedure that I have used to slowly build up a supply. I aim for 2-3 days storage for potable water. I live in a single family dwelling with a well. My intent is to be able to supply for short term blackout conditions. I also am working out a solution for off-grid water acquisition. Behind the house is a stream that doesn't run dry and I have filters and treatment means that will suffice for anything not hazmat related. (anything hazmat related would require evac to better digs anyway)

Don't yet have a generator for running the well pump. Still weighing the options (Solar vs diesel etc.)

Have considered a rain water cachement system and found many well thought out ones on the net for DIY or purchase. Expensive but relatively useful here in the NH, USA where there is decent monthly rainfall totals.

Food:
Always buy an extra can of soup or dinty-moores beef stew or Mac&cheese or beef-a-roni stuff when shopping and store it next to the water supply in the basement. When the wife takes off to her mothers or sisters I have something easy to eat and the stocks rotate well. I probably have more than a weeks rations there for the whole family (four people - two are young-uns and four cats - In an emergency I won't be feeding the cats in the summer as they are good hunters anyway) If the situation goes much beyond a week I will be kicking into one of my long-term plans many of which involve relocation. As a member of the local emergency response network (Emergency comms as a HAM and EMS as an EMT-basic) I will be involved / supported during medium range -( till the infrastructure completely disolves under the strain) For real long term societal collapse I have other plans but they are a bit off the track for this forum.