Are there certain foods that should be avoided when you have polycythemia vera?

Iron rich. Iron rich foods may help if avoided but if symptomatic treatment is advisable.
Not likely. No specific foods but usual treatment for pv is regular phlebotomy to induce iron deficiency and limit rbc production. Taking iron supplements would defeat this strategy. Also, if your diet was very, very rich in iron-protein, e.g., liver, kidney, blood sausage, etc, then you also defeat the strategy of phlebotomy to control the rbc level and run the risk of inducing gout attacks as well.