You can only steal items that weigh a total of 10 stones or less. If you steal a pouch (the weight is 1 stone) the contents of that pouch must weigh 9 stones or less to be stealable.
There are many items in the game you can steal - weapons, armor, rares, etc. Here is a list that will hopefully be continously updated to show how much something weighs, and if you can steal it or not. Items in Bold are too heavy, and items in <font color=blue>Blue</font color=blue> are blessed and can't be stolen directly.
<font color=blue>Armor and Shields</font color=blue>
Bascinet 127 - 5 stones
Bone Arm Plates - 2 stones
Bone Gauntlets - 2 stones
Bone Helm - 3 stones
Bone Leg Plates - 3 stones
Bronze Shield - 6 stones
Buckler - 5 stones
Chainmail Coif - 7 stones
Chainmail Leggings - 7 stones
Chainmail Tunic - 2 7 stones
<font color=blue>Chaos Shield - 5 stones </font color=blue>
Close Helm / Close Helmet - 5 stones
Heater Shield - 8 stones
Helmet - 5 stones
Kite (Metal) - 5 stones
Kite (Wooden) - 7 stones
Leather Armor (Female) - 1 stones
Leather Bustier (Female) - 1 stones
Leather Gloves - 1 stones
Leather Gorget - 2 stones
Leather Leggings - 4 stones
Leather Shorts (Female) - 3 stones
Leather Skirt (Female) - 1 stones
Leather Sleeves - 2 stones
Leather Tunic - 7 stones
Metal Shield - 6 stones
Norse Helm - ? stones
Nose Helm - 5 stones
Open Helm - stones
Orc Helm - 5 stones
<font color=blue>Order Shield - 6 stones </font color=blue>
Plate Armor (Female) - 4 stones
Plate Helm - 5 stones
Platemail (Breastplate) - 10 stones
Platemail Arms - 5 stones
Platemail Gloves - 2 stones
Platemail Gorget - 2 stones
Platemail Legs - 7 stones
Ringmail Gloves - 2 stones
Ringmail Leggings - 15 stones
Ringmail Sleeves - 15 stones
Ringmail Tunic - 15 stones
Studded Armor (Female) - 6 stones
Studded Bustier (Female) - 1 stones
Studded Gloves - 1 stones
Studded Gorget - 1 stones
Studded Leggings - 3 3 stones
Studded Sleeves - 4 stones
Studded Tunic - 1 stones
Wooden Shield - 5 stones
<font color=blue>Weapons</font color=blue>
Arrow - 1 shaft, 1 or 1 feather 1/10 stones
Axe - 4 stones
Bardiche - 7 stones
Battle Axe - 6 4 stones
Black Staff - 6 stones
<font color=yellow>Bola -- -- 4 bola balls, 3 leather -- Unknown </font color=yellow>
Bolt -1 shaft 1 feather - 1/10 stones
Bow - 7 stones
Broad Sword - 6 stones
Butcher Knife - 1 stones
Cleaver - 1 stones
Club - 9 stones
Crook, Shepherd's - 2 stones
Crossbow - 7 stones
Cutlass - 8 stones
Dagger - 1 stones
Double Axe - 8 stones
Executioner's Axe - 8 stones
<font color=yellow>Gargoyle's Pickaxe - stones (unknown)</font color=yellow>
Gnarled Staff - 3 stones
Halberd - 16 stones
Hammer Pick -9 stones
Hatchet - 4 stones
Heavy Crossbow - 9 stones
Katana - 6 stones
Kryss - 1 stones
Large Battle Axe - 6 stones
Longsword - 7 stones
Long Sword (Thin) - 1 stones
Mace - 14 stones
Maul - 14 stones
Pickaxe - 11 stones
Pitchfork - 10 stones
<font color=blue>practice weapon (rare) - 1 stones </font color=blue>
Quarterstaff - 4 stones
Scimitar - 5 stones
Short Spear - 4 stones
Skinning Knife - 1 stones
Sledge Hammer - 9 stones
Smith's Hammer - 8 stones
Spear - 7 stones
Two-handed Axe - 8 stones
Viking Sword - 6 stones
War Axe - 8 stones
War Fork -9 stones
War Hammer -10 stones
War Mace - 17 stones
<font color=blue> Items and Other Misc Things</font color=blue>
a backpack - 3 stones
a bag - 2 stones
Barrel - 25 stones (Closed or open)
Bear Mask - 5 stones
Basket (Empty Fruit basket) - 1 stone
<font color=blue>Black Dye Tub - 10 stones (Reward Tubs can't be stolen)</font color=blue>Pre-Patch tubs can (Rare though!)
Bracelet - 1 stone
<font color=blue>Bottle of Pink Champagne - 1 stone</font color=blue>
Bucket - 5 stones
<font color=blue>Bulk Order Deeds - 1 stone </font color=blue>
<font color=blue>a champagne glass - 1 Stone</font color=blue>
<font color=blue> checks (Gold Checks) - 1 stone</font color=blue>
Copper Wire - 5 stones
coupon for a free hair restyling - 1 stone
crates (small, medium, or large) - 1 stone
Crystal Ball - 10 stones <font color=blue>(The Future Telling Balls are blessed)</font color=blue>
<font color=blue>deed for a holiday tree - 1 stone</font color=blue>
Deer Mask - 4 stones
Dried Herbs/Onions/Flowers - 1 stone
Dye Tub - 10 Stones
Earrings - 1 stone
Empty Tub - 1 stone
<font color=blue>Ethreal Statue (Horse, Llama, Ostard) - 1 stone</font color=blue>
<font color=blue>Fireworks Wand - 1 stone</font color=blue>
Forged Metal - 5 stones
Full Jars - 2 stones
Fruit Basket - 5 stones
Fur - 10 stones
Horseshoes - 5 stones
<font color=blue>Holiday Bells - 1 stone</font color=blue>
<font color=blue>holiday timepiece - 1 stone</font color=blue>
<font color=blue>House deeds - 1 stone</font color=blue> (Can be stolen if it's a deed from a redeeded house)
Iron Wire - 5 stones
<font color=blue>Jaana's Hangover remedy - 1 stone</font color=blue>
Gold piece - 1/50 stone.
Gold Wire - 5 stones
Light - 1 stone
<font color=blue>Pile of snow - 1 stone</font color=blue>
Pillow - 1 stone
a pouch - 1 stone
Power Scrolls - 1 stone
Rings - 1 stone
Rock - 1 stone
Rocks - 1 stone
Rope - 20 stones
Scattered Hay - 1 stone
Ship Key - 1 stone
Silver Wire - 5 stones
<font color=blue>Snow Globe - 10</font color=blue>
Tribal Paint - 1 stone
<font color=blue>Whispering Rose - 1 stone</font color=blue>
<font color=blue>Wristwatch - 1 stone</font color=blue>