Seems like Gatorade bottle would ample.

1/2 gallon plastic milk jug with the open cut a bit to enlarge it.  The handle is a must.

Did you get that from a hospital bed?

Lots of people don't have wetsuits with a relief zipper. They either admit to just peeing in their wetsuit or they lie and say they don't.

Now that I have a relief zipper suit i just aim in the general direction of a scupper hole and go for it. Maybe a little water splashed over the area to wash it down and good to go. Don't over think it. It's just piss. With a little practice you can do it very nonchalantly where no one even close by realizes what is going on.  Very helpful for tourney days

I bought some of this stuff once and saved the bag, very tough bag, fairly big opening, and rolls up small to save space when not in use. 

These Stax chips containers work pretty well. Drawback is the lid is only a snap on type so it could pop off if you throw it around too much. I've only used it in the car where I had a secure place to set it.

Wow- this topic is EPIC----- after years of a wetsuit-- pee time-- I do now have a new out fit & pee in a OJ bottle- NOW it's time for a little John or a wide mouth bottle. WOW --- life is Good - thanks NCKA.