There are some spam issues in the comments, so I had to disable comment editing for a short time. It'll be back once the spam bots are gone. FYI... they leave a comment with "great" and then edit in the spam stuff later, to get around the filter.
("sich+Acc mitsetzen" - technically, the word can be used if someone decides to sit down as someone else does it. It's NOT for sitting next to someone... just for sitting down at the same time as some sort of "joined activity". Aka.... NOT COMMON ;)!)
2.
to also bet, to bet along
(Either placing down a bet along with someone or placing down some stake along with other stakes. Think of someone betting his Ray Ban along with the money. Not as rare as the first meaning but still... not really something to "learn".)