This thread is rather timely for me, since we have just had on of the worst* power failures ever in England.
This did not directly affect me, since firstly the power was only off short term where I live, and secondly I generate my own power from wind and solar.

Tens of thousands lacked power for many days.

I visited friends in the affected area and took them supplies, as they were very poorly prepared.

My observations were
1)FOOD One large supermarket remained open by generator power, many small shops opened during daylight only.
Fast food shops mostly shut, but a few stayed open and were extremely busy.
Perishables in short supply due to lack of refrigeration, plenty of non-perishables, certainly no general food shortage or anyone going hungry, even the ill prepared.
Beer and soft drinks readily available though not cold.
Most pubs shut, but some open.

2) WATER, public water supply working fine, as normal. Only those in tall buildings lacked water due to local electric pumps.

3) FUEL, no retail petrol or diesel in the affected area as filling stations lacked power to pump fuel. Supplies short immediatly outside affected area due to increased demand. 10/15 miles away supplies normal.
Bulk supplies by road tanker readily available.
LPG cylinders unavailable, these not much used in the UK so stocks probably limited anyway.
Kerosene and disposable lpg bottles unavailable.

4) COMMUNICATIONS local radio station of air, national broadcasts unaffected.
TV broadcasts as normal, but no cable TV.
No broadband internet in most areas, though dial up worked.
Direct dial landline telephones worked fine (though few people believed this since they had only cordless phones that require power)
Cellphone reception very poor, no power to masts.
Satelite phones of course worked fine.

5) LAW AND ORDER anecdotal evidence suggests an increase in thefts, despite substantial extra police patrols. AFAIK no serious disorder resulted.

After the first day, batteries, flashlights, generators, extension cords, candles, kersosene, lanterns and the like were almost unavailable, most other goods readily available.

The supplies I took to friends consisted entirely of flashlights, batteries, lanterns, and glowsticks.
Whilst this was a potentialy serious incident, I feel that some people overreacted to local shortages of perishable foodstuffs and batteries.
All these items being in plentifull supply in areas nearer central London, which was only a 30 minute train ride away.

* how serious a power cut is open to debate, but I believe that this was one of the worst in England.
We have had longer cuts, but these have affected only small numbers in isolated rural areas.
WE have also had a power cut affecting many millions of people, but it was only for about an hour.