It's funny that I don't have a membership to Costo but I end up either eating food bought from there or tagging along with friends and buying groceries from there or taking advantage of their many available free food samples; you can easily get full off of all the samples.
Costco is a membership club where you pay a yearly membership fee. The majority of items you buy in bulk which works out cheaper per unit/serving. The reason why I don't purchase a membership is because it's just me and my hubby so there's no need to buy in bulk and I don't have the storage space to keep extra stock.
I can however appreciate the many benefits it offers: groceries (they have THE best store brand - Kirkland), prepared foods (pizza and rotisserie chicken are my favorites), electronics (big screen tvs), baby equipment, fresh plants and flowers, even a massage chair.
It's a HUGE warehouse so if you get tired or hungry you can hang out at the food court where you can find bargains like a large cappuccino for $2.99 and a 1/4 lb all beef hotdog combo with 20oz pop with free refills for $1.50!
Quick lines and friendly cashiers; you'll need to put your own groceries in your own reusable bags or you can take their used boxes like at No Frills. Keep your receipt in hand when you leave because they'll be staff to take a look at it. I wouldn't recommend going during peak hours unless you don't mind the crowds and fighting for a parking space.