Just updating with a couple of decent subs for those in the UK who may have trouble finding decent substitutions:

Best chocolate plant milk I've found is Oatly, good and creamy. Though there are a number of good chocolate milks in rice, soya and coconut versions.

Best cream substitute I've found is also Oatly (Tesco, Waitrose and Holland & Barret stock). Plain tasting so ideal for savoury dishes.

Best egg-free mayo I've found is Tarragon & Chive by Plamil, ask your local health food shop. Tangy and rich, pretty good as alternatives go. A slight plasticky back note (a bit like lower fat kinds of mayo have) but it's not prominent.

Best dairy-free cheese I've found is Violife. Available from Tesco. Block or sliced. Slightly nutty flavour. I prefer the sliced version as it's easy for sandwiches.

Tesco also stock a fairly decent own-brand range. I like their 'cheddary' spread on crackers, as well as the herby 'cream cheese'. The plain yoghurt is also quite good, though a tad thin.

Best dairy-free butter sub I've found is Pure Sunflower (no trans-fats or chemical additives. Available in all major supermarkets.

Unsweetened soya milk is pretty good for most things. Though almond milk is better if you dislike the chalky flavour characteristic of soya. Get unsweetened for savoury dishes.