If you want a higher chance of rare items to spawn, you could change them at the .json files… Make sure you got a backup of the original file.
The code should look like this:
{
"type" : "item_group",
"id" : "kitchen",
"items":[
["aluminum_foil", 25],
["chips", 65],
["fried_seeds", 15],
["cereal", 50],
["cereal2", 60],
["cereal3", 45],
["toaster", 20],
["microwave", 20],
["multi_cooker", 1],
["clock", 10],
["hat_chef", 2],
["jacket_chef", 2],
["kernels", 35],
["pot", 25],
["pot_copper", 15],
["pot_canning", 15],
["pressure_cooker", 5],
["bowl_pewter", 25],
["teapot", 15],
["pan", 25],
["waffleiron", 25],
["pastaextruder", 10],
["can_sealer", 5],
["knife_butter", 90],
["knife_steak", 85],
["fork", 90],
["spoon", 90],
["glass", 20],
["glass_plate", 20],
["glass_bowl", 20],
["ceramic_plate", 10],
["ceramic_bowl", 10],
["ceramic_cup", 10],
["knife_butcher", 10],
["cookbook", 35],
["rag", 1],
["hotplate", 10],
["popcan_stove", 5],
["flashlight", 40],
["extinguisher", 20],
["whiskey", 16],
["bum_wine", 10],
["drink_rumcola", 8],
["drink_screwdriver", 8],
["drink_wild_apple", 8],
["long_island", 2],
["wine_riesling", 6],
["wine_chardonnay", 10],
["wine_cabernet", 10],
["wine_noir", 2],
["syrup", 20],
["sweet_sausage", 2],
["coffee_syrup", 10],
["roasted_coffee_bean", 10],
["bacon", 25],
["bleach", 20],
["ammonia", 24],
["flour", 60],
["yeast", 50],
["molasses", 15],
["milk_powder", 15],
["cornmeal", 40],
["powder_eggs", 20],
["granola", 5],
["protein_powder", 15],
["dry_meat", 10],
["dry_fish", 10],
["dry_veggy", 10],
["dry_fruit", 10],
["fchicken", 25],
["lunchmeat", 10],
["bologna", 10],
["nachos", 50],
["nachosc", 10],
["nachosm", 10],
["nachosmc", 2],
["oatmeal", 50],
["toastem", 30],
["toastem2", 30],
["toastem3", 35],
["toasterpastryfrozen", 20],
["brownie", 30],
["cooking_oil", 20],
["fruit_leather", 15],
["sugar", 40],
["lemonade_powder", 15],
["salt", 40],
["pepper", 30],
["cinnamon", 15],
["tea_raw", 10],
["coffee_raw", 15],
["funnel", 50],
["vac_sealer", 10],
["seasoning_italian", 25],
["seasoning_salt", 25],
["cookbook_italian", 25],
["family_cookbook", 6],
["brewing_cookbook", 4],
["chips2", 65],
["chips3", 65],
["pizza_veggy", 8],
["pizza_meat", 8],
["pizza_cheese", 8],
["cheeseburger", 8],
["hamburger", 8],
["fish_fried", 8],
["fish_sandwich", 8],
["sloppyjoe", 8],
["hotdogs_frozen", 8],
["corndogs_frozen", 8],
["heatpack", 60],
["can_beans", 40],
["pork_beans", 40],
["can_chicken", 40],
["can_tomato", 40],
["cooked_pumpkin", 20],
["con_milk", 20],
["can_corn", 35],
["can_spam", 30],
["can_pineapple", 30],
["can_peach", 30],
["can_coconut", 10],
["can_sardine", 14],
["can_tuna", 35],
["can_salmon", 25],
["can_chowder", 35],
["can_herring", 30],
["broth", 15],
["soup_veggy", 15],
["soup_meat", 15],
["soup_chicken", 15],
["soup_mushroom", 15],
["soup_tomato", 15],
["soup_dumplings", 15],
["curry_veggy", 15],
["curry_meat", 15],
["curry_powder", 15],
["chilly-p", 10],
["spaghetti_raw", 40],
["lasagne_raw", 40],
["macaroni_raw", 40],
["noodles_fast", 30],
["ravioli", 25],
["sauce_red", 20],
["sauce_pesto", 15],
["bread", 14],
["cornbread", 7],
["flatbread", 7],
["crackers", 20],
["grahmcrackers", 20],
["marshmallow", 20],
["biscuit", 12],
["hardtack", 2],
["mayonnaise", 35],
["ketchup", 35],
["mustard", 35],
["soysauce", 25],
["horseradish", 15],
["honey_bottled", 35],
["honey_glassed", 35],
["peanutbutter", 35],
["jar_glass", 50],
["jar_3l_glass", 40],
["cheese", 40],
["cheese_hard", 5],
["can_cheese", 8],
["yoghurt", 8],
["pudding", 10],
["vinegar", 15],
{"item": "veggy_pickled", "prob": 8, "charges": 2, "container-item": "jar_glass_sealed"},
["jar_sauerkraut_pickled", 5],
{"item": "meat_pickled", "prob": 4, "charges": 2, "container-item": "jar_glass_sealed"},
{"item": "fish_pickled", "prob": 6, "charges": 2, "container-item": "jar_glass_sealed"},
["lutefisk", 1],
["tongs", 25],
["char_smoker", 25],
["lawn_dart", 10],
["dehydrator", 15],
["flask_hip", 5],
["lye_powder", 5],
["sm_extinguisher", 10],
["atomic_light", 1],
["atomic_lamp", 1],
["coffeemaker", 10],
["atomic_coffeepot", 2],
["dog_whistle", 5],
["dogfood", 20],
["catfood", 20],
["salted_fish", 15],
["charcoal", 5],
["soap", 70],
["detergent", 50],
["dry_beans", 40],
["dry_rice", 40],
["survnote", 1],
["cookbook_sushi", 5],
["scots_cookbook", 6],
["food_processor", 30 ],
["eclipse_glasses", 1],
["thermos", 15],
{"item": "meat_canned", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "veggy_canned", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "apple_canned", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "can_tomato", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "fish_pickled", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "human_pickled", "prob": 1, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "meat_pickled", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "veggy_pickled", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "fish_pickled", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "sauce_red", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"},
{"item": "kompot", "prob": 4, "charges": 12, "container-item": "jar_3l_glass_sealed"}
]
}