Minecraft wiki entry for Superflat_survival, associated text: Glowstone Dust - 4 glowstone dust makes a glowstone block, which is your second light source.
Redstone Dust - Almost useless as redstone contraptions are very limited due to no stone for redstone parts. You can throw it away.
Sugar - Can be used to make some food items, such as cake and pumpkin pie, but you can't get milk bucket or pumpkins early. You can throw it away.
Glass bottles - Useless early on, only useful when you get bees. You can throw it away.
Sticks - Use for crafting Iron Tools and Ladder
Spider eyes - Emergency food source.
Gunpowder - Almost useless as the only use is TNT. You can throw it away.
Potions - Healing can heal you if your health is low while swiftness can help you escape. Fire Resistance is almost useless as there is no nether. The only use would be if you set on fire, but the only way you can set on fire is by fire aspect tool, flame bow, attack by burning mob or by lightning and you can put out the fire with water faster than drinking a fire resistance potion. Water Breathing is also almost useless, unless you drown in the water you placed. If you get Fire Resistance or Water Breathing, you can throw it away as you won't need it and it only takes up inventory space as potions aren't stackable.