Depending on your particular condition you may find that even being suppressed your immune system is pretty active against incoming infections. It will also depend on the type of medicine you are using and what protein inhibitor or T-cell mechanism it uses.
As above, most people will be more than fine. I'm immuno-Suppressed and I'm a school teacher and also coach 4 nights per week, so there is no way to avoid the contact of 100's / 1000's of people every week. Some basic precautions like being conscious of hand shaking, sneezing as well as proximity to people that are showing obvious signs of being sick etc... Rubbing eyes, touching your face etc... as some others have said.
Personally I have never been sick while being in Florida (touch wood!) and we go 1-3 times per year for 2 weeks at a time. The risk is always there of course, so one way of potentially mitigating it is to go at the end of your treatment cycle prior to getting your meds, this may make you the most uncomfortable but would potentially create a situation whereby your immune system is at its strongest, as opposed to going right after treatment. But again, this all depends on your medicine, your treatment intervals, whether it is stacked with other medicines such as Methotrexate etc...
I'm happy to discuss further in private message if you like, its an area of specialty for me based upon my various roles and education.