Liquid Seasoning

I use Maggi Liquid Seasoning, which is effectively just Hydrolysed Wheat. It's purpose is as a flavour enhancer, having a strong umami taste.

Substitution

If you can't find this locally, you can use a 50/50 mix of light soy sauce and Lea & Perrins sauce to approximate the flavour. You can also try substituting with powdered all-purpose seasoning. A commonly avaliable version of this is Knorr Aromat All-Purpose Seasoning (basically MSG and salt with a couple other spices).