My favorite new gear has been the 100% merino wool base layers I've picked up. They're so comfortable I wear them frequently, and they work. They insulate very well, wick well, and still insulate when wet. They don't overcool like the Underarmour I've got. Best hunting gear bucks I've spent in the last 2 years.
Find a quality make and stock the sizes you wish to carry, this stuff sells itself once someone has experienced it. I've not found any thats cheap, but its money I'm glad I spent.
Also, get some real Stanley vacuum bottles, the big 2 quart ones too. I don't see them around much, but they're the best of breed. Nobody likes wasting cash on substandard bottles, that first cold coffee or tea buggers up your day. They back their warranty too; I got a replacement from them recently on my 2 quart/1.9L bottle.
Quality, quality, quality. Find the good stuff and stock it. Avoid the junk. If every product you have in your store works well it will reflect well on you. Customers will have faith in your recommendations. You will also have less problems with returns if you don't stock things that will underperform.
Think of some well respected store brand products that never put their name on crappy merchandise. Two come to mind for me : Lee Valley Tools 'Veritas" line of tools, and Costco's 'Kirkland' line. They aren't goods you'll stock; but the quality model is a good reference. I have no qualms buying new to me products from either of these lines.