Crawlers cook quickly in the sun, and really should be iced down during the summer. There is a better choice. Fortunately for us, walleyes love leeches. Fortunate because of all live bait, leeches are about the easiest to keep and transport. Leeches will keep for a week or more this way if you just change the water every four hours and keep them in the shade.
Leeches are wonderful for tipping jigs.
They are also deadly fished unadorned. Not only is yarn light in weight and small for packing, it attracts walleyes in dark water and it holds liquid fish attractant. Toss in a couple cord stringers, a fillet knife, and a pair of needle nose pliers. Landing nets are a nuisance on portages and largely unnecessary. These lakes are typical Canadian Shield waters - rocky and cool.