Below you will find a link to USA Swimming. They have a ton of wonderful information all geared towards swimming and the foods your swimmers should eat.
Also on this page is a list of stay in the bag snacks that will give a healthy boost before practice.
USA Swimming - Nutrition Center
Stay-in-the-Bag Snacks for Swimmers
By Jill Castle MS, RDN
Even the most organized, well-planned swimmer can put nutrition on the backburner, jeopardizing access to essential fuel sources when he needs it most. Thankfully, some food items can stay in the swim bag, providing relief in situations where optimal food sources may be scant or not ideal.
The following snacks require no refrigeration, are temperature tolerant and provide a great fuel source. Remember to clean out snacks in the swim bag periodically and when the swim bag sits out in extremely hot temperatures. Always do a visual check and review the package label for expiration information and storage considerations before consuming.
Nuts and Nut Butters: Nuts provide a calorie kick and a boost of healthy fat and fiber in just a small handful, ormixed nuts (small) about 1 ounce (150-200 calories, depending on the type of nut). Store individual packets of nuts or a small canister in the swim bag.
Prepackaged squeeze packets or small cups of nut butters also offer a quick source of energy and pair nicely with crackers or pretzels. They can be squeezed directly into the mouth too! Flavors include peanut, almond, chocolate hazelnut, honey peanut, and more.
*Be conscious of potential swimmers with nut allergies. dried fruit (small)
Dried Fruit and Fruit Puree: Better than a “fruit snack,” dried fruit is a concentrated source of carbohydrate usually without added sugar. Try sealed bags or individual boxes of raisins, dried cherries, apricot, or mango. Squeezable fruit puree packs are another option, and offer interesting combinations of fruit such as strawberry and banana, or kiwi, strawberry and beet.
cheerios (small)Dry Cereal: Go for small boxes or make your own baggie of dry cereal. If you’re interested in low sugar types, opt for original Cheerios, Kix, Post Spoon-Size Shredded Wheat, or Kashi 7 Whole Grain Puffs. Better yet, mix and package dry cereal beef jerky (small)with dried fruit and nuts for a homemade trail mix.
Beef Jerky: Low fat, lean meat cured into a chewy, salty, protein pick-me-up—stow a re-sealable package in the swim bag. Looking for a jerky with no additives or preservatives? Try Trader Joe’s, Costco or Whole Foods brands.
Pretzels: Variety and portability are the appeal here—you can find all shapes and sizes, with salt or without, and even whole grain, flavored or not. Choose small packages so they stay fresh, or bag your own.
Fig Newtons: These cookies have been around forever (more than 100 years!) and are loaded with carbohydrate and the natural fiber from figs, providing the athlete with a sweet boost to the taste buds. Fig Newtons come in small packages of two or four cookies, and also come in strawberry and raspberry flavors if fig isn’t your thing.
Sandwich Crackers: Go for the whole grain types with peanut butter or cheese. Individual packages of six sandwiches starring the whole grain cracker are the healthiest bet.
Seeds: Sunflower, pumpkin, chia and sesame are just a handful of seed types that offer vitamin E, fiber, protein and zinc. They are nutritious and delicious on their own or mixed into trail mix, homemade granola bars or atop cereal and salad. Opt for seeds that are already hulled and come in a re-sealable bag.