If I am late for the sacrament and the bread has already been served, is it ok to just take the water?
The sacrament is a complete ordinance meant for the cleansing and renewing of covenants.
Would it be okay to be baptized without receiving your confirmation? Without both, it is incomplete.
The same holds true for the sacrament. You should have both the bread and water for it to be a complete ordinance.
I would recommend getting to your meetings on time and listening to the prelude music. If you have trouble with this, you may want to join the ward choir if they practice before the meeting begins.