Paranoid and Ready
What to consider

Two to four weeksOf ordinary household spending. One week in the house is the floor.
Mix the notesSmall and mid notes to spend: a large note buys nothing when the till has no change. Keep the bulk of the reserve in large notes, because that is the part that has to be hidden or carried.
Check on it regularlyCount it, keep it current, and adjust the amount as your ordinary spending changes.

Your own, firstThe currency the shops around you actually price in. Everything else is secondary.
Dollars or eurosThe two that are recognised and exchangeable almost anywhere, which is what makes them worth holding as a second line.
The nearest border'sOnly where one is genuinely used nearby. A currency you cannot spend or exchange locally is paper.
Why hold twoOne currency losing value, or becoming hard to move, is the reason a reserve exists at all.

Split it upThree or more places, plus one in each go-bag and one in the car. One discovery should not cost you everything.
Secure and trustedA bolted safe for the bulk, concealment for the rest. Both are covered below.
Not insuredCash at home is not covered by deposit insurance. Check your household policy's cap before deciding how much to hold.
Nothing is fully secureDoing something beats doing nothing, and preparing beats being caught out.

Safes

Home safe, 50 to 100 litres Free-standing and bolted to a concrete floor. Holds documents, cash and a modest amount of metal in one place, which is where a household safe starts. 50 to 100 LBolts down1 hour fire See on Amazon
Fireproof file chest UL Classified for thirty minutes and ETL verified against water. Hanging files inside, and light enough for one person to carry out of the house alone. 30 min ULHanging filesPortable See on Amazon
Fire and water safe The gasket seals under immersion as well as against heat, which is the rating that matters once a fire is out and the water is still standing in the room. 1 hour fire24 hour waterGasket seal See on Amazon
Cabinet safe with shelves Nearly a hundred litres on removable shelves, so folders stand upright instead of stacking. Reaching the bottom shelf does not mean unloading the top one. 3.47 cu ft30 min at 1700FRemovable shelves See on Amazon

Concealment

Picture frame wall safe Hinged behind a framed print, shallow enough to sit flush on a plaster wall. The oldest trick there is, which is why it is also the first place searched. Behind art8 x 10 inShallow See on Amazon
Under-bed locking chest Flat enough to live under a bed frame and heavy enough to be awkward to carry off. A combination rather than a key, so there is nothing to find first. Under bedDual combinationSteel See on Amazon
Wall clock safe Wall clock safe A working clock with the back half hollowed out. Hung high, which is the one plane in a room that people scan past rather than stop and search properly. Working clock10 inchWall height See on Amazon
Air vent safe A vent cover that opens, set between the studs among vents that actually work. A dead vent in a row of live ones is the tell, so it goes where nobody stands. Vent coverBetween studsCombination See on Amazon
Outlet wall safe A real faceplate over a box set between the studs. Nothing is wired to it, which is the point and also the tell if anyone tries to plug something in. Between studsReal faceplateFlush See on Amazon
Book safe Book safe A hollowed hardback on a shelf of hardbacks, which is the only place it works. Beaten by anyone who pulls the books out, so it holds a decoy, not the lot. Decoy layerHardbackShelf blend See on Amazon
Diversion can or jar Weighted to match the product it copies and kept among identical tins. Weight is what gives the cheap ones away, so it wants a cupboard nobody rummages in. WeightedKitchenAmong identical See on Amazon
Magnetic key and stash case A steel case on a magnet, mounted out of sight under something metal. Holds a spare key or a folded note, and it is sealed enough to sit outside all winter. Magnet mountUnder metalSpare key See on Amazon
False bottom food tin A screw base under real product, kept in a cupboard among identical tins. Weight is the tell, so it lives behind the things nobody lifts down to look at. Screw baseCupboardWeight matters See on Amazon
Diversion wall socket A socket front on a magnet, pushed into a hole cut in the plasterboard. Minutes to fit and it holds a rolled note stack, which makes it a decoy, not a safe. MagneticNo wiringOne stack See on Amazon