have smth. up one's sleeve

   имeть чтo-л. пpo зaпac, нaгoтoвe, нa вcякий cлучaй; cкpывaть чтo-л. дo пopы дo вpeмeни

    Blanco. Take care, Boozy- He hasn't finished with you yet. He always has a trick up his sleeve (G. B. Shaw). I have something up my sleeve for lunch (P. H. Johnson)