What I have done is throw away the heavies (unwanted) items, like stone, until you get 300/300 or below. What you can also do if you dont want to get rid of anything that is weighting you down, is throw out of your inventory what is weighting you down, then that will allow you to get stamina back up. Then pick up the item again, walk as far as you can until your stamina depletes again and you stop, then throw out the item again...rinse and repeat, until you get where you want to go. It is hard work and very time cunsuming, but it beats throwing out items that are heavy but you want to keep, like ores that you have mined