Sliding drills, first off make sure that evryone wears long pants!
Push slide drill- a lot of people think this may be stupid but it is very effective in teaching correct technique. Space players out across the gym floor and put them in a bent slide position. They will then push themselves across the floor on one side then when they reach the other side have them switch legs and push back the on the other side.
2-Step slide- Using the bent leg slide the players will take 2 steps and slide.They will alternate legs both up and back the length of the floor.
Slide by and Head first drills can be conducted in 3 lines from about 20 feet from a base. Focus is on footwork, sliding technique and reading the fielders actions.
A drill I like that involves 5 at a time and works on cardio and skills is the 4 bases drill. If you have a facility that can allow you to set up a diamond and then add an extra 1st base and homeplate 10 feet from the original try it.
Like I said you can involve 5 players at a time and cover most baserunning situations.
Place a BR at each original base.
Have the pitchers work from the stretch and the BR's working on their leads.
The hitters will have a bat for this drill.
The pitcher will simulate a pitch.
The hitter on the original plate will take a full swing and run out a double.
The hitter on the additional plate will bunt for a hit and run to the additional first base and then move to the original first base.
The first 3 BR's will have advanced two bases each.R1 is now R3. R2 will have scored as will R3.
With the closest hitter now on 2nd and the additional hitter now on 1st.
The bases are once again full and will allow the scenario to continue with the next two hitters now moving into their respective boxes.
Just something else to think about.