Food Hacks - Ingredient Substitutes

Mr Cake was making some hot cross buns this evening and realised that we hadn't bought any more mixed spice since I used the last of it in mine last week - so (Google is my friend) I searched to see what it's made of. "Mixed spice" seemed unlikely to be the name of a single spice - unlike allspice - and sure enough, it's made from a bunch of others, which we did have - so we made some. There are lots of things like that - little substitutions you can make - so today's post is dedicated to a couple of the things I've tried with success when I've run out of or forgotten to buy something.

Buttermilk
Plain, unsweetened yoghurt makes a good substitute for buttermilk; otherwise, add 1 Tbsp of white vinegar or lemon juice to a cup of milk (multiply to whatever ratio is required for your recipe) and leave for 5-10 minutes to curdle. This won't make as thick a product as the real deal but I have used it with success in recipes. You can also use yoghurt and some milk or even water in a squeeze to top up milk in a recipe.

Honey
A cup of honey in a recipe can be replaced by 1 1/4 cups of sugar and 1/4 cup of liquid - water, or a liquid already included in the recipe. Keep in mind this will only serve the sweetening function, and won't lend the delicious honey flavour to your baking, but it will work in a pinch.
Mixed Spice (found here)

Mix together;
1 Tbsp cinnamon
1 tsp ground coriander
1 tsp nutmeg
1/2 tsp ground ginger
1/4 tsp allspice
1/4 tsp ground cloves

Self-raising Flour
This is a bit contentious - the generally accepted ratio is between one and two teaspoons of baking powder for every cup of flour. I have always used one and have never had a problem, but if you're wanting, say, extra fluffy scones you may want to err on the higher end.

What ingredient substitutes have you used when caught short mid-recipe?