Please go ahead and refrain from purchasing all products certified kosher. This includes products made by:
Kellogs
Campbels
Starbucks
Hidden Valley
Smart USA (aluminum pans, etc)
Coke
Pepsi
Gatorade
Nestle
Heinz
Subway (not all but some of their restaurants are certified kosher)
Tropicana Juices
Target's Archer Farms and Market Pantry
Walmart's Great Value
Orville Redenbacher
Del Monte
Hunt's tomato sauces
In fact, almost all major food producer companies have at least some products that are certified kosher. So, if you're worried that companies which choose to have products certified kosher might support Israel, you better be safe and not purchase any commercial food products.
You should also be careful because Israel is a major exporter of fresh vegetables. Israel is also at the forefront of developing new domesticated fruits and vegetables so don't by things like cherry tomatoes (developed in Israel), Jaffa oranges (developed in Israel), dragon fruit, and countless other fresh produce items.
You should also be aware that Israel is at the forefront of technological development. As such, you want to stay away from:
Microsoft products
HP products
Apple products
Motorola
Any company that uses voice prompt phone systems.
Any company that uses Amdocs customer database systems.
This isn't even touching on the medical developments that come out of Israel.
Good luck living a decent life. :)