What kind of hand drum? Why, they all will work nicely. Frame drums.darbukas,djembe,bongos,(my fave) will all work wonderfully. Cajons also belong here and they have the added benefit of providing something for you to sit on.
If you don't feel like bringing a drum for whatever reason,there are also other percussion instruments that are even smaller and will add an exciting accent. Castenets, an afuche,maracas, or a guiro can enhance the groups sound as a whole. They can be easily placed in a tote bag or backpack. Claves played softly (they can be really loud) can be used. I don't recommend tambourine as they are usually loud and jangly. If you happen to be jamming where there's a conga drum present,those can also be played as long as the drummer focuses on staying behind the ukes volume wise.
What's key is keeping the beat,also known as the pulse. That's the most important thing you can do. A simple, rhythm keeping beat that people can follow with ease is far more impressive than doing super fancy playing. Remember you're there to enhance the uke music.
Some of my favorite drum companies are Toca,Meinl,and for bongos,Tycoon. Their Ritmo series are absolutely wonderful and can be found used on sites like eBay and Reverb. Just make sure the heads are in good playable condition and that there's no cracks in the actual drum. You may want to get a bongo stand as your legs can get sore from playing them between the calves. I also prefer a stand as it enables the tone to project better and also if I want to switch to uke or castenets,etc I don't need to set the bongos on the floor.
If you have back problems I highly suggest a bongo stand and would also suggest not playing cajon as it requires that you bend over it to play it.
Just starting out? Try playing along with music you're familiar with no matter the genre. I jam with my Alexa unit regularly,asking her to play songs in several different genres. Recently I discovered I have a knack for cha cha music on my bongos. Martin Denny is another fave I jam to, in addition to Booker T & the MG's, Hugo Montenegro and some disco music.