Stealing a single sweet from the pick-&-mix selection is a criminal offence, so stealing £100worth of goods most definitely is!
CRB checks (which are now actually DBS checks, because the name of the relevant agency has changed) show all convictions and cautions. They are never removed from the record (although, due to a legal challenge that may change in the future).
However (in England & Wales) only certain employers have access to CRB checks. (e.g. where the employment involves working with, or alongside, children or vulnerable adults). Most employers have no access to CRB checks.
Even so, you need to remember that it's also a criminal offence ('fraud by false representation') to lie about whether you've got any criminal convictions when asked to declare them (unless the convictions are spent under the terms of the Rehabilitation of Offenders Act which, assuming you receive a fine, won't be for 5 years). That offence usually carries a prison sentence.