It’s not immediately intuitive but having a coffee or espresso mid workout is amazing. It’s got no sugar, no carbs, and no calories. The effect is nearly instantaneous. It’s cheap and plentiful. It doesn’t take up a lot of volume; you don’t feel bloated afterwards.
Sure it’s a mild diuretic but you tend to drink so much water during a work out it doesn’t matter.
One of my favourite ways to do it is split my exercise into two 45-60 minute halves and in the middle have a nice double espresso. It’s civilised and energising.
Of course having a bulletproof coffee just before exercise is a different matter for a different post.