For safety reasons, I always wear lace up running shoes on the plane, (no longer inconvenient with pre check!) and pack one pair of dress shoes if going for work and one pair of casual going out shoes ( for me that's a pair of Maisins I got in Spain since they squish to flat). If summer I can squeeze in a pair of flip flops too. Depending on the purpose/length of trip, I can skip the Maisins and just use the dress shoes, especially if short on space.