Hydration vest on race day?

I'm debating whether to wear my hydration vest on race day. Is that a terrible idea? I'd love to not have to wear anything extra, especially since the forecast is looking frustratingly warm for this time of year.

But, here's what I'm thinking:

• I'm a heavy sweater, and dehydration is what killed me last time.
• I've always used one on my long runs, and practiced taking a drink at every mile mark.
• If I didn't wear it, where do I keep my gels, salt tabs, phone, and headphones (to blast some motivational music for the last 6 miles)?