Melt 3 Tbsp. butter in a buttered Dutch oven over low heat. Add 1 (10 1/2-oz.) package miniature marshmallows, and cook, stirring occasionally, until melted. Remove from heat. Meanwhile, process 1 (15-oz.) box honey-almond-flax multi-grain cluster cereal, in batches, in a food processor until finely ground; combine with 3 cups crisp rice cereal, 1 (6-oz.) package sweetened dried cranberries, and 1 tsp. salt. Stir into marshmallow mixture. Press cereal mixture into a buttered 15- x 10-inch jelly-roll pan. Let stand 1 hour. Cut into 40 (1 1/4- x 3-inch) bars.
Cook's Notes: For testing purposes, we used Kashi GOLEAN Crunch honey-almond-flax cereal. For easy travel, layer bars with parchment paper in disposable plastic containers with lids.