Today I needed to merge 40 ~600Mb .pcap files into one humongous capture file.
Since I was doing this server sided and I'm a tcpdump.org kind of person, I installed tcpslice.
tcpslice - extracts pieces of and/or merge together tcpdump files
Using tcpslice, I simply did:
root@privato:~/traces# time tcpslice *.pcap -w full.pcap
I could have used the mergepcap from the Wireshark package, but I didn't have wireshark installed, and as I mentioned, I'm a tcpdump kind of guy ;).