you have slacks? black pants that you need to iron type of pants...
wear a dress shirt, the ones with buttons. for shoes, maybe some heels but not too high. you definitely need to dress nice to get those type of retailer jobs because they expect you to be representing their store front.
see the black pants in the pix - http://cdn.thegloss.com/files/2007/11/metallic-top-slacks-pumps.jpg
you don't have to wear a blazer but it'd be nice...
if you can shop at forever 21 or H&M these things can be pretty affordable.
for a shirt - http://www.milaneze.com/illustr/goodphotos/mediumimages/Burberry+Long+Sleeve+Trendy+Dress+Shirt+For+Women+White+g_5565_38386.jpg
or if u don't like slacks you can do skirts, but not too short - http://s7.thisnext.com/media/largest_dimension/F4395798.jpg