Headphone mini to line level

Hi there,
I am a guitarist and wish to take the smallest equipment to replicate my favourite guitar tone to various amateur live venues. My ideal equipment is a small ‘guitar headphone amp’. This unit plugs into my guitar and has a mini headphone jack output. Designed to practise at home. I assume I can send this into an ‘aux’ input in a venue’s mixing desk, but if they don’t have this option then how can I send it to one of the main line level inputs?