What are the most effective ways to utilize a flask to carry hot nutrition options like soup or tea during cold weather rides, considering the constraints of limited storage space and the need for easy access during rides? How can riders balance the weight and bulk of a flask with the need for warmth and nutrition during extended periods in the cold? Are there any specific flask designs or materials that are better suited for cycling applications, such as insulation, durability, and leak-proofing? What are the pros and cons of using a flask with a built-in heating element versus relying on pre-heated liquids? How can riders safely consume hot liquids from a flask while in motion, and what are the best practices for avoiding spills and scalding? Are there any alternative solutions to flasks that can provide similar benefits, such as thermoses or vacuum-insulated containers? What are the key considerations for choosing the right type and size of flask for a given ride, and how can riders optimize their nutrition strategy to stay warm and fueled during cold weather rides?