Getting weird resitance drops with an FSR and a raspi using a MCP30
It looks like the change (drift) in voltage is pretty slow, maybe due to temperature changes in/at the resistors?

An easy (software) solution is to take the differential of the voltage over time and compare that value to a threshold.

In other words, compare each sample taken to the one before, and if the difference between them is, say, > 20% you have detected a significant change (i.e. object put onto/removed from the table).

To suppress more noise, you may want to vary the scheme by, e.g., having a running average of the last n samples and compare each new sample to that average; or have two running averages, one of the samples n...m and the other one of m+1...current and compare those. This averaging basically creates a low-pass filter and the window sizes should be chosen so as to suppress as much noise as possible while still giving a useful amplitude for your signal.