It's common knowledge that taller people are more successful. This effect is also pretty strong - for instance, tall people make an average of $789 per inch per year and this has been shown repeatedly in a set of four large-scale salary survey studies.
We don't know that it's causation, but it seems very likely that people judge others' general fitness, consciously or not, by looking at their height (which makes evopsych sense, considering for instance that malnutrition decreases height).
I can think of two ways to Goodhart this (are there more?): you can improve your posture, or you can raise your feet off the ground using elevator shoes or heel lifts, giving you say 2'' (which is $1,600 per year, plus nonmonetary gains) for less than $20.
It's not as cheap as platform shoes, but it would be economically beneficial and very munchkiny to get limb lengthening surgery. Even a modest 2 inch procedure would easily pay itself back in 10 years.
Cost: $10,000 in India +incidentals
Benefit $800 x 2 x 10 years = $16,000.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.