Variety, variety variety!!! We have LDPE (low density polyethylene) and HDPE (high density polyethylene) bags depending on what type and feel you like. A LDPE will feel soft and look glossy, where as a HDPE feels crinkly but is extremely strong. Plastic shopping bags at Coles and Woolworths are HDPE but can hold a fair weight in them.
Black bags are really suited if you don't want other people to view what is in the bag, whereas the coloured bags are bright and fun and most of them have at least 2-3 different sizes so your shop can have 2-3 different sizes and you can put small items into a small bag and larger items into the larger bags. Much more economical to use the correct bag for the size item that you are selling.
They are sold in packets of 100 or if you are needing more, then there is better pricing for larger quantities. Take a look, I don't think you will be disappointed.