I've never had a problem with leaving my chips on the table in order to take a break. If I plan to be away for longer than a quick bathroom break (5-10 minutes), I'll tell the dealer and also check on the time limit. I would definitely take any possessions as well as put your large denomination chips in front or under a stack of smaller chips. It's kinda scary the first time you leave hundreds of dollars at a table of strangers. And poker degenerates at that.
Some places will allow you to be gone for an hour, some base it on the number of dealers that cycle through while you are gone, and some count the number of absent buttons you collect (usually one per new dealer). You can also double check with the floor if the dealer seems confused.
Usually, the room is okay with a quick meal break (30 minutes to an hour). But if you plan to be away longer, you should cash out and come back later.
If you come back after cashing out, don't expect your seat to be available.
They will not save it for you. You will most likely have to get back on the list and wait for the next available seat. You can request your old table (or any specific one you prefer) and wait for that table to have an opening.
If there is no list (no waiting players) and you return, you still might not get your old table. The floor wants to balance out the number of players at each table, so that might keep you from going back to your original table if they are just short one player while another table is short two players.
There are some time limits (either 1 or 2 hours) about when you can return to a specific game and
NOT buy in for the same amount you left with from that game. For instance, you leave the 1/2 NL HE game with 800 and come back 20 minutes after cashing out. You are then required to sit down with 800. Now, if you are gone for two hours and return, you can buy in for what you want under the min/max rules. If you return after 20 minutes and go to
another game (either a different game or a different limit) you can buy in for what you want under the min/max rules.
It's a bit different if you bust out/felt on a table.
You can usually ask the dealer to "lock up" your seat and then you have some time (I've never heard it well defined) to go get money/shake the money tree and to return to the same table. The amount of time you have seems to depend on how much you spew
and how many players are waiting to grab that spot.
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I have been guilty of leaving for way too long and having my chips scooped up by the floor. When that happens, ask the floor for your chips. They'll have them up front and safe.
It's a good idea to stretch your legs every now and then. Take a quick walk around the area or go and grab a coffee.