We consider tissue P systems working on vesicles of multisets with the very simple operations of insertion, deletion, and substitution of single objects. With the whole multiset being enclosed in a vesicle, sending it to a target cell can be indicated in those simple rules working on the multiset. As derivation modes we consider the sequential derivation mode, where, if possible, one rule is applied in a derivation step, and the set maximally parallel derivation mode, where in each derivation step a non-extendable set of rules indicating the same target cell is applied. With the set maximally parallel derivation mode, computational completeness can already be obtained with tissue P systems having a tree structure, whereas tissue P systems even with an arbitrary communication structure are not computationally complete when working in the sequential mode. Adding polarizations — only the three polarizations [Formula: see text], [Formula: see text], [Formula: see text] are sufficient — allows for obtaining computational completeness even for tissue P systems working in the sequential mode.