Some things that I think a coach shouldn't buy even if they have the money is for wind suits and sometimes bags are alright, but sometimes they just get too big and ugly looking. I don't think a coach should buy wind suits because most of the time your players are going to be hot as it is. However, I think it's nice to have sweatshirt with the team name on it and sometimes sweatpants too, but none of that swishy stuff! Then sometimes bags are alright just keep them small though so you don't have a ton of space in them after everything it put in them. One thing I think would be appropriate to buy if you had the money are volleyball practice uniforms. I think volleyball practice uniforms would be great so parents don't have to wash a million different pairs of clothes or if you wear them during warm-ups for a game, your regular jersey won't get as sweaty.
Besides buying volleyball practice uniforms, you could buy adidas volleyball socks, well if that's the brand you wanted. Also, you'll use the same women's adidas volleyball shoes for practice and games, at least I hope so because you don't need 2 pairs of shoes!