It depends on the product.
Most non-emulsion liquids (shampoos, wheel cleaners etc) will not really go off unless you were to expose them to something that they should not be exposed. So keep out of direct sunlight, avoid extreme heat or cold and you should be fine. If a product is un-opened, it is even less likely that there would be an issue. Often, even if the product is exposed to this and separates, it can be recovered by bringing back to a sensible temperature and giving it a really good shake.
Emulsion products will be more sensitive. It will take less temperature extreme to cause them to fall apart and they may not go back together when shaken. You may get them to go together, but you should be aware that the emulsion size you achieve with a shake is much larger than that achieved with high shear mixing, which would be how they have been made. What this means is that the product will be less stable going onwards and may well perform rather differently. Emulsions will also tend to degrade more rapidly, even in ideal conditions. So if you leave one sitting on a shelf for 3 years, there is a fair chance that it will have gone off and the above would apply.
Thickened emulsions or creams will tend to be more stable than their less viscous counterparts. However you still have to take the same care and the same issues may apply if they do go off.
Solvent based products will typically be quite stable and the main issue with sealants, for example, would be moisture which can cause them to cure in the bottle (contrary to common belief, it is NOT the oxygen which is the problem). Temperature extremes here are more likely to be a health and safety issue than causing a lot of stability issues.
Waxes... I would be inclined to say that extremes should be avoided here too. I know that there is a tendency for people to store them in the fridge but I would not really recommend this. If nothing else, this means that the wax will be cold when you open it, moisture will then condense on the surface and can potentially cause issue (waxes commonly contain the same sort of things found in sealants - they can moisture cure, so beware).
As a rule, we would not quote a lifetime longer than 2 years. There are too many variables beyond that (but, assuming good storage, yes, this will be conservative).
