How to create ICMP filters with both type and code ?

The capture filter you are probably thinking of is:

icmp[0:2]==0x0301

But to be more descriptive, you could use something like this instead:

icmp[icmptype]==icmp-unreach and icmp[icmpcode]==1

Note that the compiled BPF code isn't exactly the same though. It seems that the first format is slightly more efficient, taking 2 fewer instructions.

Compare icmp[0:2]==0x0301:

(000) ldh      [12]
(001) jeq      #0x800           jt 2    jf 10
(002) ldb      [23]
(003) jeq      #0x1             jt 4    jf 10
(004) ldh      [20]
(005) jset     #0x1fff          jt 10   jf 6
(006) ldxb     4*([14]&0xf)
(007) ldh      [x + 14]
(008) jeq      #0x301           jt 9    jf 10
(009) ret      #65535
(010) ret      #0

to icmp[icmptype]==icmp-unreach and icmp[icmpcode]==1:

(000) ldh      [12]
(001) jeq      #0x800           jt 2    jf 12
(002) ldb      [23]
(003) jeq      #0x1             jt 4    jf 12
(004) ldh      [20]
(005) jset     #0x1fff          jt 12   jf 6
(006) ldxb     4*([14]&0xf)
(007) ldb      [x + 14]
(008) jeq      #0x3             jt 9    jf 12
(009) ldb      [x + 15]
(010) jeq      #0x1             jt 11   jf 12
(011) ret      #65535
(012) ret      #0

Refer to the pcap-filter man page for more information.

(If instead you're looking for a Wireshark display filter, then refer to pfuender's answer.)