sorry I wasn't very clear!!!!

I want the ability to check in the 50lbs of luggage in my suitcase on my way back. I'm not going to bring a suitcase filled with 50lbs weight there. ( I do however need to bring stuff for the wedding that I would not normally need, and also some warmer clothes as I'll be in yosemite, tend to get fairly cold easily) Therefore.... I am wanting to know what dimensions of a suitcase I should bring that would fit that much? Does that make sense?? This is to avoid the scenario of needing to drag back 2 suitcases because the one I am bringing there doesn't actually have the capacity to fit up to 50lbs. ( and for instance only fit about 36lbs or something ( not great with these conversions here)

I'm hoping to check one suitcase, with one carryon on the say from SYD-JFK-NYC. In that scenario, I'm hoping that I only have to check the same in on the way back because my shopping will fill up the suitcase. ( I go from NYC-SFO, then SFO-SYD on my return)

I will probably be bringing some presents back and dont' know how much space they'll take? I am bringing a few over, mainly some aussie foods for some friends who live there/relies.

So I guess I'm wanting some recommendation in terms of luggage sizes/brands as I feel the one I have lent is probably too small and wouldn't actually fit up to 50lbs if I were to stick to one suitcase checked in on my way home, after I have done my shopping. I'm expecting to just lift my luggage onto a trolley and be picked up afterwards, and hopefully avoid checking in two.

I've started some pre-packing. Actually pulled out all summer gear.

Thank you so much for the link - I'll have a look at that now!