Hi Gabby,
It is totally up to you whether you purchase new walking shoes or use trainers. As long as they are comfortable for you then that is all that matters. The only thing I would suggest is that if they are new trainers/walking shoes, try and wear them in first. You wont want any nasty blisters to jeopardise your holiday.
I hope this has helped, If I can help you with any other advice, please get in touch.
Warm wishes,
Cheryl, your editor