I didn’t submit any for the application and was not asked to provide additional in that regard but it’s usually at the visa counter you might get that question. In which case always best to have ‘best onward ticket’ ready imo
£30 for the 60 day visa (extendable to 90 day) it’s a chore with 12 pieces of paper work but once you do it they granted mine in like 2 days. Easy money. Flying out soon (from UK).