If you have a boat, remember to gas up on the road before getting to your destination, as marina gas prices are much higher. Same thing for snacks and drinks to have out on your boat, grocery store prices will be cheaper than convenience store or bait shop/marina prices.
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Boating doesn't have to be a pricey business. You don't have to go to the high-priced marine stores for most of your needs. My husband gets everything at the regular hardware store when he can - it's cheaper.
You can even save dollars on boating - In a well known marine store I saw boat curtains for $22 for a panel. We used bargain valance ruffles from the dollar store and instead of $100+ for curtains, we got easily installed ones that are perfectly good for $5!