How one can be aware without any object? To be aware or mindful means to be aware/mindful of something, isn't it? Therefore, in the context of Buddhist meditation one can choose an object like breath or body and fix attention on it or be aware of it, while it changes from moment to moment (in-breath/out-breath, body sensations etc.). One can also be aware of the "present moment", which means not focusing on anything specific, but maintaining open field of awareness and registering whatever enters that field (again: breath, body sensations, but also sounds, thoughts, emotions, internal commentator, smells, tastes etc.). Anything that natural flow of our everyday experience brings to us. And then comes in the other element you mentioned, our reactions to these experiences, which can also be an object of our non-judgemental awareness. Observing these reactions is much more beneficial than focusing only on the experiences of the so called first order. By becoming aware of these reactions we first of all see which one of them increase our frustration and which one contribute to our inner peace. By learning that, we can slowly start changing these reactions and thus transforming our life.