What about eating and/or smoking just after temporary veneers have been put on?

Temporary Veneers are placed on the teeth to protect them while the permanent veneers are being made at the lab.  They are not at all like the permanents will be and are not very strong nor very resistant to staining.  I would recommend you avoid smoking if possible, but if you do smoke you could use pure baking soda as a dentifrice to help to remove stains which will undoubtedly form on the temporary veneers.  As far as eating I would advise using a knife and fork for everything you eat and avoid using your front teeth to bite or chew with.  The good news is that you will probably have your permanent veneers in a short time.