"And [David] took his staff in his hand, and chose him five smooth stones out of the brook, and put them in a shepherd's bag which he had, even in a scrip; and his sling was in his hand: and he drew near to the Philistine." (1 Samuel 17:40)
Just as God used David & the sling to kill Goliath, just as God used David and his arp to calm the furious king Saul, He can use you with anything you have, as simple as it may be. You just need to be willing to give your all to God.
You can be big or small, weak or strong, pray and God will be with you and win your battles.